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  #1  
Old 06-28-2016, 12:45 PM
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Default Jump to the lands... Question

I am prepping ladder tests for my 6.5 Creedmoor build with various bullet combos. Generally with gas guns, the general consensus on the interwebs was to "load to magazine length" because generally to get to or near the lands, would require an OAL greater than would feed from a magazine. Right now with a Hirtenberger 120g PSP I can easily find / exceed the lands from a PMAG. With my 140g Matchburners I will be able to soon find the lands when I receive my Knights Armament SR25 magazine (they load out to 2.880 supposedly).

Even though I this is a semi-auto, are there and recommendations for bullet jump for initial load testing? 2 thousandths jump? 1 thousandth jump? No jump?

I know that messing with the seating depth will be the last step in load development, but want to try and get it as close as possible from the start.

...and yes I am measuring from O-Give with bullet comparator, not COAL.
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Old 06-28-2016, 1:13 PM
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You can't always get to a 1 or 2 thousands jump in a semi-auto chamber - especially with a light bullet combo. Some chambers are too long. This is why some of us just set to magazine max length and fine tune the powder type and charge level. Set it just off the lands (2 thous) if you can and go from there. Jump is sometimes not that big of a factor in finding a decent load in a semi-auto.
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Old 06-28-2016, 1:57 PM
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The rule of thumb in general is that you should initially seat the bullet as long as possible and still allow the rifle to function. With mag fed semi's the magazine is the determining factor. Once you start at the longest possible length you can start seating the bullet a little deeper for refinement of your load.
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Old 06-28-2016, 1:57 PM
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Originally Posted by robert101 View Post
You can't always get to a 1 or 2 thousands jump in a semi-auto chamber - especially with a light bullet combo. Some chambers are too long. This is why some of us just set to magazine max length and fine tune the powder type and charge level. Set it just off the lands (2 thous) if you can and go from there. Jump is sometimes not that big of a factor in finding a decent load in a semi-auto.
Thanks... With the 120g bullets surprisingly I can get to the lands. They are a flat base Bullet so I have more freedom to load them further out. The 140g boat tails I can only reach the lands once I get the new magazine. Pmags are about 5 thousandths off what i would need.

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Old 06-28-2016, 2:48 PM
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I am the fan of knowing the distance to the lands; I am the fan of 'the running start', I want my bullets to have that jump. If my rifles are not accurate with bullets jump/the running start the rifle does not leave the house. I have no infatuation with sticking the bullet into the lands. I want my bullets to hit the lands 'a running'.

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Old 06-28-2016, 4:20 PM
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I just measured. Nosler 140g Custom Competition and the Hirtenberger 120g PSP could both touch the lands while still working with a PMAG (kept under 2.800COAL), the Barnes Matcher Burners need about 4 thousandths more room for the PMAG but should fit in the Knights Armament magazine.

I'm glad I checked because magazine length particularly for the 120g PSP would have jammed hard into the rifling either causing setback or wouldn't possibly chamber.
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Old 06-28-2016, 6:18 PM
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I am the fan of accuracy. I am the fan of using whatever length works best wether into or out of the lands. I am the fan of letting the rifle determine what that length will be.
That said this.
The rule of thumb in general is that you should initially seat the bullet as long as possible and still allow the rifle to function. With mag fed semi's the magazine is the determining factor. Once you start at the longest possible length you can start seating the bullet a little deeper for refinement of your load.
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Old 07-12-2016, 8:56 AM
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I have another question... I measured 10 bullets from same lots using the comparator and got a decent spread on OAL to lands. I have noticed that most online videos or tutorials show measuring only once and that's the measurement to determine your jump.

Would I be better served basing my jump off the average measurements or just pick on and go?
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Old 07-12-2016, 9:33 AM
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When your after extreme accuracy you want all your seated rounds within 0.001
If you measure and find a lot of variation it's time to sort your bullets into like groups.
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Old 07-12-2016, 9:42 AM
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Is there a minimum amount the bullet should be seated into the neck?

I have a Tikka T3 in 6.5x55 that has LONG throat. I can seat the bullet so far out before hitting the lands that I start to seat them without the bullet being seated all the way through the case neck and into the body of the case.

How would you proceed here? Rule still apply? Thanks.
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Old 07-12-2016, 9:50 AM
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As someone who had shot competitive Service Rifle for several years, I will say that tweaking distance to lands in a gas gun is not going to yield much practical gains.

If you're shooting a traditional BTHP (aka Open Tip Match) bullet, the bullet is going to be very jump tolerant.

That being said, my primary bullet for the 600 yard line was the Berger 80gr VLD and I was seating .010" into the lands, and I was chasing throat with that load (I would make my 600 yard line ammo the week or two prior to the match). I only did this mainly because of word of mouth (that VLDs are seating depth sensitive) and for peace of mind. But I literally shot some VLDs that were about 18 months old (seated them nearly a year and a half prior to a match) and so they were definitely jumping to the lands. Yet, I still shot a 196-12x in 15mph wind.

Personally, when it comes to ammo that's going into a magazine, I'll settle on a COL based on that magazine, and develop my loads based on that COL. After you decide on a load, you could try and mess with seating depth, to tweak that load further, but I feel it is just a waste of time. Granted, reloading is a hobby in itself, so if you have the time and desire, go for it.

My advice is to stick with a quality BTHP/OTM, or try the Berger hybrids which are becoming all the range with F-Class shooters. The Berger hybrid is supposed to be a blend of traditional BTHP/OTM and VLD, giving the higher BC of VLD, but the jump tolerance of BTHP/OTM.
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  #12  
Old 07-12-2016, 10:37 AM
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Quote:
Originally Posted by ocabj View Post
As someone who had shot competitive Service Rifle for several years, I will say that tweaking distance to lands in a gas gun is not going to yield much practical gains.

If you're shooting a traditional BTHP (aka Open Tip Match) bullet, the bullet is going to be very jump tolerant.

That being said, my primary bullet for the 600 yard line was the Berger 80gr VLD and I was seating .010" into the lands, and I was chasing throat with that load (I would make my 600 yard line ammo the week or two prior to the match). I only did this mainly because of word of mouth (that VLDs are seating depth sensitive) and for peace of mind. But I literally shot some VLDs that were about 18 months old (seated them nearly a year and a half prior to a match) and so they were definitely jumping to the lands. Yet, I still shot a 196-12x in 15mph wind.

Personally, when it comes to ammo that's going into a magazine, I'll settle on a COL based on that magazine, and develop my loads based on that COL. After you decide on a load, you could try and mess with seating depth, to tweak that load further, but I feel it is just a waste of time. Granted, reloading is a hobby in itself, so if you have the time and desire, go for it.

My advice is to stick with a quality BTHP/OTM, or try the Berger hybrids which are becoming all the range with F-Class shooters. The Berger hybrid is supposed to be a blend of traditional BTHP/OTM and VLD, giving the higher BC of VLD, but the jump tolerance of BTHP/OTM.
Thanks, I am loading up ladder tests for both Barnes 140g Match Burners and Nosler 140g custom competition. I guess I won't sweat it, but if possible will load closer to lands than not with variance included. I don't want to waste time sorting bullets, or waste time using a micrometer die to seat each one individually to their proper depth.
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Old 07-12-2016, 3:18 PM
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Originally Posted by John Browning View Post
Is there a minimum amount the bullet should be seated into the neck?

I have a Tikka T3 in 6.5x55 that has LONG throat. I can seat the bullet so far out before hitting the lands that I start to seat them without the bullet being seated all the way through the case neck and into the body of the case.

How would you proceed here? Rule still apply? Thanks.
I believe minimum seating depth is bullet diameter. So seat .264 minimum.
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Old 07-12-2016, 6:21 PM
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Originally Posted by LynnJr View Post
I am the fan of accuracy. I am the fan of using whatever length works best wether into or out of the lands. I am the fan of letting the rifle determine what that length will be.
I agree with this. I usually stick with a particular bullet, powder and primer and very seldom deviate from the bullet choice as my reamer was probably designed for a particular bullet, which is often a very high BC, quality target bullet, like Berger . Every once in a while I might try another powder or primer.

Quote:
Originally Posted by bigdawg86 View Post
I have another question... I measured 10 bullets from same lots using the comparator and got a decent spread on OAL to lands. I have noticed that most online videos or tutorials show measuring only once and that's the measurement to determine your jump.

Would I be better served basing my jump off the average measurements or just pick on and go?
Short answer, in my opinion if you are comfortable jamming a bullet, start jammed and work your way to jumping when doing seating depth. If you are not, then start 0.005" off the lands and then work backwards from there.

I can still get my guns to shoot very well and I load to a particular CBTO value and if it is within 0.001-0.003", I leave it alone. I do sort bullets and I load to the kernel and I have other processes that I feel help ensure consistent ammo. The most important thing for me is to find a load that in nearly all conditions, will shoot the best groups. This means a load that is in the middle of an accuracy node for powder charge and will also shoot well in a range of seating depths, say 0.001-0.003" variation from each other. What does this give me? It means that even if I have variations in my ammo components, I am giving myself some room to have slight variations in my ammo but will still shoot well. I do not necessarily want the load that produced the smallest group. I want the load that will agg well over multiple days because we all experience different conditions from say-to-day, and we typically pre-load for a match and there is almost never an instance where you can "tweak" a load like the benchrest guys sometimes can do.

Do a powder charge ladder test, find the middle of an accuracy node, play with seating depth and then shoot what you think are the best loads in multiple conditions and see which one aggs the best and stick with it. Then, go out and learn to read the wind.

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Is there a minimum amount the bullet should be seated into the neck?

I have a Tikka T3 in 6.5x55 that has LONG throat. I can seat the bullet so far out before hitting the lands that I start to seat them without the bullet being seated all the way through the case neck and into the body of the case.

How would you proceed here? Rule still apply? Thanks.
There is no "rule" per se. As long as the neck can hold the bullet, you're good. If your gun likes bullets jumped, then jump them. If it likes it jammed, then jam them. In general, most of my ammo is jumped because I sometimes have to eject a loaded round and I want no chance of sticking a bullet in the lands. As long as you have enough neck to hold the bullet, then you're good-to-go. All my chambers have relatively long freebores which allows me to seat my bullets long. Most of the time, the bearing surface of the bullet does not go below the neck/shoulder junction. That being said, I will jam a bullet if that particular barrel likes the bullets jammed. I just have to make sure the bullet only goes out one way

Quote:
Originally Posted by ocabj View Post
Personally, when it comes to ammo that's going into a magazine, I'll settle on a COL based on that magazine, and develop my loads based on that COL. After you decide on a load, you could try and mess with seating depth, to tweak that load further, but I feel it is just a waste of time. Granted, reloading is a hobby in itself, so if you have the time and desire, go for it.

My advice is to stick with a quality BTHP/OTM, or try the Berger hybrids which are becoming all the range with F-Class shooters. The Berger hybrid is supposed to be a blend of traditional BTHP/OTM and VLD, giving the higher BC of VLD, but the jump tolerance of BTHP/OTM.
I would follow this. In purpose built match guns, the rule of thumb is different.
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Old 07-12-2016, 6:52 PM
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For those who think seating depth doesn't matter you should give it a try sometime and see what happens to your groups.
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Old 07-17-2016, 10:22 AM
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So with my cheap hirtenberger 120g PSP I found there were two definitive bullet oal groups. One was .5950 and .6060 like they were two machines that produced this lot or mixed lot.

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Old 07-17-2016, 11:37 AM
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Originally Posted by bigdawg86 View Post
So with my cheap hirtenberger 120g PSP I found there were two definitive bullet oal groups. One was .5950 and .6060 like they were two machines that produced this lot or mixed lot.

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that is not uncommon even with modern, quality bullets like Berger or Sierra. Even custom bullets like Vapor Trails, Barts, etc will have this as well. The OAL is what I have seen vary the most. I like to point the bullets, and sort by OAL. I have weighed bullets, but stopped for now. I also do not measure base-to-ogive because I measure CBTO of a loaded round anyways and if one were to be much different than the others, I will put that into the sighter/fouler pile.

Mike Rattigan's book has a section on the so called, "superbullet". What he means by that is it is not a particular bullet, but rather the lot# of that bullet that for some reason, just flat out shoots better. And, buying that same particular bullet, but with a different lot# could be drastically different.

This is why it is critical to try to obtain the same lot# of bullets, especially when you find that one is producing better results than the other. It is not uncommon to see competition shooters buy and log multiple lot#s down in their logbook and track what lot#'s work best or show a tendency to produce better scores. It is also not uncommon that when one finds a lot# that they think is great, to buy thousands of them. I have a lot# of 105 hybrids and 180gr hybrids that are shooting great and I have 2K+ of the same lot#. This helps eliminate variables, especially when you are going through multiple barrels and trying to determine which barrel shoots better so that one is what you take to big matches.
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Old 07-18-2016, 5:20 PM
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Good to know... I simply loaded up the .6060 lot and my seating depths were infinitely more consistent. I broke down and bought a whidden micrometer seater die which made a otherwise tedious job of uniform seating depths incredibly easy. I probably won't be as OCD for subsequent loads but went for consistency since these are my ladder tests.

Barnes Match Burners don't seem to have but the occasional flyer which is slightly longer.

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Old 07-18-2016, 9:54 PM
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OK I have another "possibly stupid question"...

Looking at many many online threads... People will write .01 or .02 jump, but then call it thousandths. I'm confused.

I thought I was educated enough to know, but are people forgetting what the decimal places actually mean? Tens, hundreds, thousands?

Which is it!?

Even in my OP I interchanged them on accident



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Old 07-18-2016, 10:09 PM
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Originally Posted by bigdawg86 View Post
OK I have another "possibly stupid question"...

Looking at many many online threads... People will write .01 or .02 jump, but then call it thousandths. I'm confused.

I thought I was educated enough to know, but are people forgetting what the decimal places actually mean? Tens, hundreds, thousands?

Which is it!?

Even in my OP I interchanged them on accident



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0.500 = 500 thousandths = 1/2" - this is rarely used when talking in terms of seating depths. Maybe, you might get someone saying 100-120 thousandths off the lands (0.100"-0.120")

0.050" = 50 thousandths
0.005" = 5 thousandths
0.0005" = 5 tenths

It should be...5 thousandths (0.005") or 10 thousandths (0.010") off the lands or jammed.
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Old 07-18-2016, 10:18 PM
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0.500 = 500 thousandths = 1/2" - this is rarely used when talking in terms of seating depths. Maybe, you might get someone saying 100-120 thousandths off the lands (0.100"-0.120")

0.050" = 50 thousandths
0.005" = 5 thousandths
0.0005" = 5 tenths

It should be...5 thousandths (0.005") or 10 thousandths (0.010") off the lands or jammed.
Thank you. I inadvertently was doing the equivalent to reducing fractions with this. My mind was reading one hundredth .01, but everyone was talking ten thousandths .010 Which on paper are the same...but mentally the nomenclature had me confused for a moment

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Old 07-18-2016, 11:10 PM
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This has been a godsend on my blackout ARs. I couldnt get cast bullets made that wouldnt stick or not chamber. Ordered the Hornady OAL tool and I'm in business. Some bullets seem short but I'll just have to lower the powder throw.

From what I've read, trimmed 223 to blackout has a thicker neck than OEM blackout brass. That gives many chambering issues. I debated throat reaming the barrells to .311 so these cast will work. Gotta hit the range first before I decide to do that.
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Old 07-21-2016, 1:12 PM
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For rapid fire stages, I load the bullets to the maximum length that my magazines will take. For long range stage, I single load the rounds. I seat it anywhere from .005" to .010" from the land. The accuracy depends on the particular rifle, but usually that range will give you good starting accuracy.
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Old 07-22-2016, 6:49 AM
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Originally Posted by bigdawg86 View Post

Even though I this is a semi-auto, are there and recommendations for bullet jump for initial load testing? 2 thousandths jump? 1 thousandth jump? No jump?



...and yes I am measuring from O-Give with bullet comparator, not COAL.
I am the fan of the running start, I want my bullets to have 'that jump'. I want my bullets past the beginning of the rifling without slowing down.

Slowing down at the rifling: That is scary.

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Old 07-22-2016, 6:51 AM
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it is even scarier when it just sits there.

WAITING: For what?

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Old 07-27-2016, 6:06 PM
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If you start your bullets with a lot of jump what in the world do you think happens when they reach the bores constriction?
Do you think they accelerate when encountering an obstruction?
WOW!!!!!!
If you think the engraving force has no affect tell us why Isaac Newton got it all wrong.
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Old 07-27-2016, 9:27 PM
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Originally Posted by LynnJr View Post
If you start your bullets with a lot of jump what in the world do you think happens when they reach the bores constriction?
Do you think they accelerate when encountering an obstruction?
WOW!!!!!!
If you think the engraving force has no affect tell us why Isaac Newton got it all wrong.
Wut? I am fully aware that pressure increases as you already get closer to the rifling, but via magic accuracy does depend on this jump or lack thereof. Correct me if I'm wrong but I would imagine that the concentricity of the bullet, or bullet deformation from lack thereof when it slams into the rifling is why your groups change depending on your distance from the rifling.

Long range / precision guys please confirm or dispel this idea for me as this previous post seems like I'm missing the punch line for a joke that was never told.

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Old 07-28-2016, 4:40 AM
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When you start a bullet seated firmly into the lands it only accelerates.
When you seat a bullet with alot of jump it accelerates initially then slows down when it reaches the bores constriction then re-accelerates as the pressure builds.
Accuracy is found at both locations usually and a Shooter looking for best accuracy would start out at there longest possible length and work back in only one direction.
And if you seat long originally you won't have any pressure issues that are generally only found here on this website.
The only downside to seating long is if it causes a bullet to get stuck in the lands but most competitors will not have this problem.
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Old 07-28-2016, 9:09 AM
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I know people that have guns they shoot very long distances (I consider 1000yd, very long) whose guns/loads prefer as much as .050" of jump for the optimum accuracy.

In my personal experience, for what ever reason (likely cheap homemade guns), my best loads always are at or into the lands. I have read that jamming leads to excessive pressure, but I have never experienced it. In my albeit amateur and limited experience, the only time I get a sticky bolt is when I load over max book with a powder marginally fast for the application.

Just my experience.
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  #30  
Old 07-29-2016, 4:45 PM
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8mmFMJ 8mmFMJ is offline
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Want to hear about bullet jump?

A friend of mine dropped a .308 into my 30.06. Pulled the trigger, and dinged the steel target at 300 yards.

When he pull the the case out and grabbed for another out of the .308 box I stopped him real quick and asked what the **** was he doing! Sure enough, he had accidentally fired one of the .308 150gr's out of my 30.06.

Strong extractor eh?
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Old 07-30-2016, 7:56 PM
fguffey fguffey is offline
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Quote:
Strong extractor eh?
Quote:
A friend of mine dropped a .308 into my 30.06.
To the first part about the extractor; no, the extractor was not involved. When a 308 W round is chambered in a 30/06 the case head spaces on the case body/shoulder juncture. The case body/shoulder juncture is .014" larger in diameter than the 30/06 chamber at the contact point. Meaning the case body at the shoulder juncture must be sized before the round will chamber; it requires a small amount of effort and there are many Garand shooters just could not believe their bolt would seat the 308 W round.

When the case is extracted it looks like a short 30/06 with no neck and a very short shoulder.

You did not give the make and model of your rifle.

F. Guffey
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Old 07-30-2016, 8:06 PM
fguffey fguffey is offline
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Sure enough, he had accidentally fired one of the .308 150gr's out of my 30.06
The 30/06 shoulder is ahead of the 308 W shoulder by .388"; that means before pressure can get serious the case must fill the chamber. And then there is the distance the bullet must travel to reach the rifling.

F. Guffey

Last edited by fguffey; 07-31-2016 at 2:59 PM..
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