I ran into some very strange results with handloads last week.

First of all, I have been at this for a while.
I don't load hot. Never over book max. Never blown a primer or stuck a bolt. My cases last a long time.

Here is what happened.

7X57 in a Spanish 93 Mauser, dated 1913.
Barrel is well worn, but the action is in good shape.
Stripped bolt will not close on Field gauge or a NO-Go gauge, so I assumed head space is ok.
Throat is very, very long. 175 grain Hornady round nose is .110 off the lands with the bullet base level with the case mouth. So with the 175 seated at OAL of 3.065 we are near .520 off the lands

Factory Winchester 140 gain Power points show no pressure signs, but keyhole at 50 yds,

New WW brass with 139 Horandy SST, AA 4064 at 38 grains shoot ok No pressure signs, maybe even low pressure from looking at the primer.

Then I resized this WW bras in a RCBS full length die and tried 154 and 175 Hornady RN

154 with 35 grains AA 4064 -- I got powder blow back - in my face - not much. Yes I had on eye protection. Appears to be leaking around the outside of the case. black soot from case mouth to base of case and on botl face. Primer is OK.

Thought maybe low pressure and not expanding the case enough to seal the chamber, so I fired the gun from a distance with 36 grains - same result, then 37 grains -- appeared to seal the chamber. I was not close enough to tell for sure. Did have soot on the neck of the case.

Tried the same with 35, 36, 37 grains and the 175 RN. Definetly no blow back at 37 grains. AA Book max is 39 grains at 43,600 CUP.

So I shot 3 of the 175 wih 37 grains of AA 4064 and got a .8" 50 yd group.

I am thinking the extra long throat may have the affect of "improving " the case capacity and I am way low on the powder charge which causes the case to not expand enough to seal the chamber.

Any body seen anything like this? Could this really be a low pressure situation. What am I missing?


Thanks

just at a guess i'd say you have a barrel with not only a long throat, but maybe an erroded one as well. I thinking that the 140 gr. bullets were possibly overstabalized, and that there is a bunch of freebore in which you are loosing some of the initial pressure.

same guess as Butch + how many reloads from the brass, it could be worked hardened.
Also if the bore is worn as you stated i supect the low weight loads even at 37gr of imr 4964 may be not building enough pressure to seal the chamber.

Soot from the the neck to the head says low pressure to me.

Trigger, you are absolutely correct! The long throat has the same effect in your rifle as the freebore does in a Weatherby Magnum: It causes pressures to be much lower with regular loads in your rifle, and allows Weatherby to use loads for high velocities that could not be safely used in rifles with standard throats.

What you were experiencing were the results from firing underpressure loads, and as you noted, the cartridge cases were not expanding adequately to seal the chamber. Gas was blowing by to the rear.

In this situation, it is perfectly safe for you to increase the powder charge enough for the pressure levels to rise to where the case expands as it should, and seals the chamber.

Until you reach the point where there is no longer soot on the neck, you can still increase the charge until you stop getting soot. I'd do this workup 1/2 grain at a time, however. Stop increasing when you get the accuracy you want.

butchbloc

quote:

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just at a guess i'd say you have a barrel with not only a long throat, but maybe an erroded one as well. I thinking that the 140 gr. bullets were possibly overstabalized, and that there is a bunch of freebore in which you are loosing some of the initial pressure

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These guys from Minnesota make all too much sense sometimes.....

Personally I'm not ascribing to any "overstabilization" theories but the rest of this makes real good sense.

The keyholing power points are a complete puzzle....just forget it and either use what works or rebarrel it.

Oh...yea....GO PACKERS

how does one over stabailize something it is stable or not stable. Sounds to me that with the long throat he wasn't building enough pressure to seal the chamber. I have about the same rifle and use 139 horndays in it with no trouble. matter a fact it shoots well under a inch with them at 50 yards plenty for min. of whitetails. in the north woods.

"Any body seen anything like this? Could this really be a low pressure situation. What am I missing?"

Your bullet is moving beyond the end of the neck before you've developed enough pressure to move the brass enough to seal.The long heavy bullets with a faster powder would help. With reduced loads and slower powder gas in the face can be common with some rifles. I know this from experience. roger


Thanks[/QUOTE]

In my experiences, your rifle is worn enough that the manuals max pressures, are low in your rifle. So you have to work up. Personally I'd rebarrel the old girl myself.

However, if you want to eliminate the low pressure blow back use a faster powder. Also the longer bullets like the 175s or the 160/162 size bullets would be a good bet.

As far as keyholing bullets. I have an old worn 30/30. It doesn't not shoot any factory or regular loads from manuals very well at all. However, it does like loads with light bullets and fast powder ( SR 4759). It also loves a fast load, with a long 220 grain Round Nose.
35 grains of W 748 and a 220 gr RN.

Whatever wear problems that 30/30 is experiencing I'd dare say your 7 x 57 is along the same lines.

My 30/30 has been in the family a long time so I don't want to change it. If it had not been in the family, it would be wearing a different barrel, in a different caliber, that is for sure.

Cheers
seafire