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-   -   HXP Reduced Charges (http://forums.thecmp.org/showthread.php?t=146142)

7 ring 09-02-2014 09:34 PM

HXP Reduced Charges
 
I measured the O.A.L. and the length to ogive on 10 rounds of HXP 1978 that I pulled out of a can of mixed headstamp HXP ball I purchased from CMP. The measurements were .024" difference from long to short. Only 2 rounds measured the same and the rest were all over the board.

I pulled bullets from 32 rounds of HXP 1978 and charge weights in 9 rounds ran from 53.6g to 54.5g with the tenth round having a charge weight of 58.4g.

I thought, why not clean the asphalt out of the case mouths, measure each charge weight and reseat the bullets to increase consistency and maybe gain a little accuracy. I decided to set the charge weight at 45.0g or 84%, which I have done with other surplus ammunition with a great deal of success. The charge filled most the case behind the bullet, so I was not concerned about overpressure due to powder position inside the case.

I fired the 32 rounds yesterday and several of them had delayed ignition. I could hear the distinct sound of the hammer falling as if I was dry firing, then one or two seconds later the powder ignited. This concerned me.

Accuracy was not any better than shooting loose HXP ball with mixed headstamps.

I went back to the range today and fired 69 rounds of HXP with mixed headstamps without any problems.

Use caution if you try to pull bullets and measure charge weights to increase accuracy.

sigman2 09-02-2014 10:37 PM

45.0 grs. is a considerable load reduction given the original charge weights.

Even though this ammo is HXP 1978 they could be from different lots. The powder burning rate will vary from lot to lot so the charge weights will vary accordingly. There will always be very minor variations in the powder charge of ammo from the same lot. The powder charges are measured by volume, not individually weighed. The 53.6 to 58.4 gr. charge shows that these are from different lots.

If you take ten rounds from ten different lots and adjust the powder charge to the same weight you will have a real mixed bag of loads. Remember there were usually multiple lots run in the same year. Head stamp year does not mean the ammo is the same as far as charge weights. You need to separate your ammo by lot numbers which is not possible with loose ammo. This is why I prefer not to buy loose ammo.

7 ring 09-02-2014 11:32 PM

Thanks for the info. What you say makes sense. I never considered different powder lots in the same year of production.

I guess I am expecting too much from the mixed delinked HXP I bought from CMP. Most 10 shot groups are under 3-1/2" @ 100 yards, so I should not complain.

LazyEngineer 09-02-2014 11:38 PM

Thanks for posting this. Interesting to see that disassemble and reassembly somehow affected your primers. I cannot imagine how introduction to fresh air, or rearrangement of the powder could do that. Did you use any kind of solvent to remove the asphalt? Did you tumble them while disassembled?

Also, my advise is to not spend too much time trying to make HXP more accurate. The single most important contributor to a rounds accuracy is the bullet itself. And so long as you are re-seating the HXP machine-gun ammo bullet back in the case, it's going to shoot like cheap machine-gun ammo. Mixing ones from different lots, with random powder from different lots...

7 ring 09-03-2014 12:13 AM

Quote:

Originally Posted by LazyEngineer (Post 1148165)
Thanks for posting this. Interesting to see that disassemble and reassembly somehow affected your primers. I cannot imagine how introduction to fresh air, or rearrangement of the powder could do that. Did you use any kind of solvent to remove the asphalt? Did you tumble them while disassembled?

I pulled the bullet and trickled the charge directly from the case onto the scale.

I ran a dry brush through the case neck a few times and dumped out the dry asphalt.

I did not tumble them.

I guess I can't make a silk purse out of a sow's ear.

USSR 09-03-2014 08:26 AM

With HXP charge weights approaching the mid-50's, that indicates that the powder is slower than the IMR4895 typically used in USGI M2 ball. And, I would not load 45.0gr of IMR4895 with 150gr bullets.

Quote:

I guess I can't make a silk purse out of a sow's ear.
Yep. Best thing you could do for better accuracy is pull those FMJ's and replace them with 155gr BTHP's. The quality of the bullet used is the primary determinate of how accurate a particular load is.

Don

edlmann 09-03-2014 08:32 AM

Quote:

Originally Posted by sigman2 (Post 1148140)
Even though this ammo is HXP 1978 they could be from different lots. The powder burning rate will vary from lot to lot so the charge weights will vary accordingly. There will always be very minor variations in the powder charge of ammo from the same lot. The powder charges are measured by volume, not individually weighed. The 53.6 to 58.4 gr. charge shows that these are from different lots. If you take ten rounds from ten different lots and adjust the powder charge to the same weight you will have a real mixed bag of loads. Remember there were usually multiple lots run in the same year. Head stamp year does not mean the ammo is the same as far as charge weights. You need to separate your ammo by lot numbers which is not possible with loose ammo. This is why I prefer not to buy loose ammo.

Good reason for the variation in charges: on the production line, manufacturers use powder which is NOT conformed in its characteristics as is the powder you buy with which to reload. Rather, the loaders test the lots and adjust the charges accordingly to fit the burning characteristics of the powder in the lot they received - not a uniform standard.

ETA: There is some value to breaking the asphalt bond by seating the bullet very slightly. This would theoretically help uniform the resistance. Dunno if I'd then shoot the ammo in a Garand - might want to experiment with a bolt gun.

hamourkiller 09-03-2014 12:30 PM

One thing you can do to greatly improve your accuracy is to Mexican Match in some 150 gr target or hunting bullets. The Military FMJ just suck, any modern bullet will halve your groups. Shooters Pro shop has 155gr seconds available now.

Use a collet puller and pull the ball, resize the neck and seat the 155 CC. You will be amazed how much your groups will improve.

sigman2 09-03-2014 01:38 PM

Quote:

Originally Posted by LazyEngineer (Post 1148165)
Thanks for posting this. Interesting to see that disassemble and reassembly somehow affected your primers. I cannot imagine how introduction to fresh air, or rearrangement of the powder could do that. Did you use any kind of solvent to remove the asphalt? Did you tumble them while disassembled?

Also, my advise is to not spend too much time trying to make HXP more accurate. The single most important contributor to a rounds accuracy is the bullet itself. And so long as you are re-seating the HXP machine-gun ammo bullet back in the case, it's going to shoot like cheap machine-gun ammo. Mixing ones from different lots, with random powder from different lots...

It wasn't exposure to air or rearrangement of the powder that caused the problems. 45.0 grs. was too light of a load with the slower burning powder. The OP didn't state whether the powder was extruded or ball. If extruded it was probably a variation of IMR 4895; if ball a variation of WC 852. In .30 M2 Ball the average charge of IMR 4895 was 50.0 grs. So 45.0 grs. of a slower powder was probably way too low. (Note: This is not intended to be interpreted as a suggested load.)

Bulk powder's burning rate will vary considerably from lot to lot. Ammo manufactures will adjust the charge weight to achieve the desired velocity and pressure. When mixing powders from different lots the reloader will have no clue as to the burn rate. It's a crap shoot.

As far as I know a given lot of loaded ammo will use cases, primers, powder and bullets that are all from their own individual lots. Therefore all cases will be of a certain lot and the same goes with primers, powder and bullets.

7 ring 09-03-2014 09:09 PM

I have decided to remove the bullets from the HXP brass by placing them in 8 round clips and firing them. I can replace the bullets with something more accurate after I complete the removal process.


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