Last week I loaded twenty rounds for an old 7MM Mauser I picked up a couple weeks ago.... shot the twenty rounds, no problems...Minute of cow groups! Thought maybe the old girl didn't like Sierra 150 SBT's so I bought a box of Winchester 145 Power-points (Factory ammo), good groups but the primers in 12 of the 13 rounds fired backed out.... not a lot ,but enough to fill the difference with my thumb....WHY??

You say "an old 7MM Mauser I picked up a couple weeks ago." Precisely what kind of old rifle is it -- an old military one? Does it have a shot-out barrel? Is the chamber perhaps a bit too large or long? Does it have excessive headspace?

I think a lot more information is needed about this rifle before good advice can be given about what may be wrong with it.

LE270,
Thanks for the reply. The rifle is a 1908 DWM in good to very good condition, bore shows some wear, but for the most part looks good... has strong rifling and is bright and shiney. Brass shows no signs of a bad chamber.
Maybe an error in judgement on my part, but since the rifle looks as good as it does and is all matching numbers, I haven't checked headspace. CSJ

My call would be head space also.

If you handloaded some, did you seat the bullet out far since your rifle probably has a long throat? That or the head space problem is why it is throwing the bullets all over the place.

It has to be the barrel, not the round.
Rebarrel it and still have a great gun, one with a history. Can't buy that in a new firearm.

Check or have checked the headspace before you before anything drastic. Low pressure can cause slightly backed out primers even in rifles with good headspace.

You say 1908 so I am assuming Brazilian. Those rifles were throated for the 175 grain RNs so they have a lot of free bore for the weights you are shooting which would take pressures down. You might also slug the bore to see if it is oversized.

If there is something wrong with the barrel and you want to keep it in the original configuratation, I have an unfired barrel I squirreled away years ago. Email me if you are interested.

If the gun is collectible, all matching, you might want to try cast bullets rather than rebarrelling. With cast bullets you can match the throat and bore diameter and seat the bullets out to resolve any headspace problems. Joe S

C.S.,

The low pressure of the 7mm Mauser rounds from US manufacturers can create the backed out primer. Its probibly not a problem. But if you want to improve your loads from an accuracy and velocity standpoint, load your bullets out closer to the lands, your barrel is likely long-throated for the 175 grain military ammo. Also try H414 powder, by far the best powder for the cartridge I have found. I like the 160 grain Speer and 160 grain Nosler Partitions. Good luck

BigBullet

Seafire/B17G,
I'm checking headspace before I try anything else. I seated my reloads to Sierra....maybe to short?
Leftoverdj,
If headspace is really bad, I'll be E-mailing you about the barrel!
Joe S,
I don't know if the rifle is really collectible...I understand they made a bunch of 1908's, but I think it's pretty neat! Don't really know anthing about cast bullets.
Big Bullet,
I did a little digging around in my powder and found some H414....don't remember what I used it for...ordered some heavy RN bullets, I'll give it a try.
Thanks all, CSJ

take some electricians tape and cut out two (2) small rectangular pieces that will fit on the shoulder of an unfired round. Put this cut piece of tape on the shoulder of this unfired round. One on each side. Try to chamber the round. If headspace is good you should feel resistance when closing the bolt. If not cut two more pieces and stack them on the two that are already on your unfired round. Try closing the bolt on this one and if you do not feel any resistance you have headspace problems. Or wrong ammo!!

That's a nice handy tip, Marley.

I like the tape trick. There is also a product that goes by the name "plasti guage", or something like it, that can be found at automotive parts stores. They are little colored plastic strips that "crush", and the width to which they crush can be translated directly into a physical measurement. This will give you your exact headspace reading in .001"ths. The trick to all of this: don't let the case turn when closing/opening the bolt.

Thanks marley,
Ain't real scientific, but cheap.... I like that!
packrat,
I think you plasti-strip idea would work great even with a go-gauge. thanks, CSJ

7MM Mauser Update,
I just tried marley's little-piece-of-on-each-side-of-case trick....bolt won't close.
So I put one little piece of tape on the base and bolt closed.....two pieces of tape on the base....bolt won't close.....ain't real scientific either, but I think headspace is OK. CSJ

It could be that the rifle has excessive headspace. Have it checked by someone who has a 7X57mm NO-GO gauge!

However, low peak pressures can also cause this effect. It is often noted when shooting low-pressure, cast bullet loads. If you can believe this, what happens is that the case is actually "blown forward" by the primer a little upon firing, actually shortening the head to shoulder length. Then, when normal peak pressure occurs, the case is "restreched" back to normal dimensions, and the proturding primer is reseated fully into the pocket. However, if pressures are sufficiently low, the reforming does not occur, and you have a protruding primer when you extract the case. This is one of the reasons why it is often recommended that once a case is used for a reduced or cast bullet load, it should only be used for such ammo thereafter. I think this could happen with a cartridge that is sufficiently underloaded by the factory. The 7X57 is generally one of these in U.S. ammo, BUT I don't know how much underloaded your ammo may be. Maybe enough for this to be the problem, maybe not!

Check the headspace!

C.S.
I have also seen the back out primer on light cast bullet loads and on US loaded 8x57mm Mauser loads. The primer backing out on lightly loaded ammo is not uncommon. One thing you can do though is neck size your cases so they fit your chamber perfectly, then headspace will not be an issue.

BigBullet

If this rifle were mine and I were trying to get it to shoot well, once I had satisfied myself that it is in good shape and is strong, I'd try working toward full-power loads to see whether it will begin to group well with such loads. As you probably know, some rifles don't shoot well with reduced loads. Unfortunately -- because of all the unworthy and questionable old 7X57 rifles out there -- American factory loads in this cartridge are usually very much underpowered.

I'd try a number of different bullet weights -- say 140, 160, and 175 grains -- and different powders, and then refine the loads using the bullet and powder that gave me my best results in my first tests. Going to Steve's pages and seeing what powder he recommends as likely to give the best results for a given bullet weight -- or going to a reliable loading manual that gives similar recommendations -- is a good place to start.

l think BIGBULLET is right about low powered factory ammo being the cause...l have a 8mmm that l NOW load for...prior to that l used winchester ammo...every case the primer backed out...read in a book about this...now every reload with a bit more "omph" has the primer staying put

Eleguello,
Sorry if this is a really stupid question.... but, do you think the two pieces of tape on the case head is too inaccurate a method to check headspace? I don't remember, I think a no-go gauge is only .004-.006 larger than a go guage.
BigBullet,
I just go a new set of RCBS FL Dies, do you think I could resize 2/3 the neck with them and get the same results?
LE270,
Thanks, I added Steve's pages to my favorites and ordered some 175 gr. SP....a good place to start.
Toyota,
Thanks for the reply....once I'm sure the headspace is OK, I'll add the "omph". CSJ

just a small note... my loads are not maximum, though it may have sounded that way... ex-mil ammo has a higher velocity...l prefer accuracy over speed... good idea to have the headspace checked anyway
cheers

C.S.

The main thing about the neck sizing is that you don't set the shoulder back on the case. That way the case fits the chamber perfectly(using fired brass)I use a sharpie pen to mark the neck and slowly lower the die until it just reaches the bottom of the neck.

The idea behind partial neck sizing is so the bullet is centered in the chamber. There may be some resistance to closing the bolt. I have tried this with other calibers, but not the 7mm. Either my shooting wasn't good enough or it had no effect on accuracy in my rifle. I load mostly for hunting purposes, so I want the cases to feed smoothly, so sizing the entire neck makes sense for me. The partial neck sizing is prevalent in target shooting, so there must be something to it. You mention 2/3 or 66% of the neck to be sized. What I have read is that 80% of the neck is sized. Maybe it has something to do with holding the bullet firmly?.

Good luck and hope this helps,
BigBullet

Toyota,
I'm with you on the accuracy over speed!

BigBullet,
My thinking on sizing only part of the neck was to keep from touching the shoulder, marking the shoulder with a marker and sizing as much of the neck as possible..... might work?? Thanks for your help. CSJ

I have P-17 that had headspace questions,now rechambered.I found a low pressure load will shorten the case and protrude the primer,a mid-level load will leave the case as is and protrude the primer,and a normal load will flatten the primer much more than the presure would warrant and stretch the case.All case were Lee trimmer length.

My full-length resizing dies will resize a case about a thou undersize.I crazy glued shim stock to the base of a resized case before buying a No-Go.

C.S.J.,

I recommend having the headspace checked before proceeding, but as others have pointed out it may just be due to lower powered loads or a underspec factory case. I once bought a box of Remington factory .222 and every one backed out the primer in my perfectly headspaced chamber.You didn't mention if your handloads backed out primers. I assume they didn't. That would seem to support the mild load and/or underspec case theory.

I shoot an identical rifle and have found that the 139 grain FMJ NC 7x57 FN ammo offered by SAMCO(2,712 fps) shoots pleasantly to point of aim and is quite accurate(1 1/2 inch). You can shoot it for what it costs to reload. Remember too that the rifling twist in your 1908 is 1 turn in 8 1/2 inches, so accuracy with bullets lighter than 154 grains will only be fair if you push velocity. These bullets will shoot fine if you load around 2,600 - 2,700 fps.

[ 11-07-2003, 06:08: Message edited by: Bobster ]

C.S., I found that in several 7X57mm rifles, if I used a new, unfired case and PARTIALLY seated a primer in the pocket, when I put the case thus prepared in to the chamber and closed the breech, the primer DID NOT seat fully! It still protruded slightly. I don't know how thick the electrical tape is, nor what the headspace would be on the case you'd be putting the tape on. If a new case, it would be a little short, naturally, since max case dimensions can't exceed min. chambers if the ammo is going to chamber at all!

I think using the proper gauge is the only way to know for sure.

C.S.Justice,
I just fired 38rds of the same Winchester ammo and not one of the primers protruded.
I had trouble getting mine to shoot(8" groups),
I rebedded it,full floated the barrel, still sprayed bullets, finally I cut a 1/4" off the barrel and that made all the difference in the world. The first three shot group went about 5/8"
1908 Brazilian. Good Luck.And have the headspace checked.
Stepchild

downwindtracker2,
Thanks for the reply. My handloads were close to upper mid-level and the primers were flatten a little.
Bobster,
Primers in the handloads never backed out.... just really bad groups. Once I resolve the headspace issue I may check out the Samco ammo
eldeguello,
I think the tape idea was wishful thinking on my part..... I'm ordering a no-go gauge, thanks.
Stepchild 2,
Thanks for the reply, sounds like I can't the Winchester ammo....I hopeing to not do anything to the barrel.... but I'll cross that bridge after I check the headspace. CSJ

Mr. Justice, I'd also check the barrel crown, to make sure it is not marred, if accuracy seems to be a problem. Sounds like that was stepchild's problem. If there's damage, and it is confined to the crown area only, the barrel can be recrowned without giving up any barrel length...

[ 11-10-2003, 20:21: Message edited by: eldeguello ]

eldeguello,
I didn't remember anything wrong with the crown..... so I got it out of the safe and looked really close , no dings and everything looked uniform at the muzzle. Thanks, CSJ

[ 11-11-2003, 02:54: Message edited by: C.S. Justice ]

Perhaps all electricians tape is not created equal!!

How thick is the electrician�s tape that you used to check headspace?

Can not remember the rule, but seem to think if less than .005 headspace would be OK.

If you buy the guage let us know how it checks out. My guess, based on your use of the electricans tape is that it is OK. But.... if the tape was made in China...................

marley,
I headspaced a .308 barrel I installed on an old VZ-24 a few years ago with a go-gauge and a piece of clear scotch tape....it has over 3,000 rounds through it now.
eldeguello really got me thinking..... a lot of variables with brass.... I ordered a no-go gauge from Brownells. I'll let you know how it turns out. Thanks, CSJ

[ 11-11-2003, 06:32: Message edited by: C.S. Justice ]

C.S.
You can't always tell by looking. I once had a 700 Varmint that wouldn't group. I did everything I knew to it and nothing helped, my gunsmith suggested cutting and recrowning the barrel, after that it was a shooter. The barrel didn't show any flaws.
Stepchild

stepchild 2,
After I'm sure of the headspace I'll try some different loads and see what happens.... bought some 175gr SP for starters..... if I can't get it to group with them I may try recrowning. Thanks,CSJ