Compensating brass volume with more/less powder.

[InTheWeeds]

I was curious if it was wise to try to compensate larger brass volume with more powder to get a more consistent velocity spread? If so is there a formula for figuring it out? I have some Hornady brass that is varying over 5 grains weight difference. I know the weight of the brass is not directly related to its volume (i.e. the weight can come from a thick head) but I'm looking to see if I just get in the ballpark to make a lot of 100 handloads have a low ES.

 

[ChrisGarrett]

Re: Compensating brass volume with more/less powder.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: In da weeds</div><div class="ubbcode-body">I was curious if it was wise to try to compensate larger brass volume with more powder to get a more consistent velocity spread? If so is there a formula for figuring it out? I have some Hornady brass that is varying over 5 grains weight difference. I know the weight of the brass is not directly related to its volume (i.e. the weight can come from a thick head) but I'm looking to see if I just get in the ballpark to make a lot of 100 handloads have a low ES. </div></div>

I don't know of any formula, because as you note, that extra weight might come from other things.

Just segregate the brass into batches which are more uniform, if you must.

There are other methods to use to get your ammo into, or near, single digit SDs, if that's really going to matter.

Chris

 

[vman]

Re: Compensating brass volume with more/less powder.

Best suggestion would be to batch your brass and go from there. That would be more solid than any voodoo formula, which I have not heard of.

Generally people say to drop the powder charge back for mil-surp brass, and that is where the safety issue is. Brass of the same make with slight variations is less prone to giving you pressure issues provided your not riding a thin red line.

But if your after single digit ES/SD, regardless of how good the brass is, you would want to weigh sort them.

 

[InTheWeeds]

Re: Compensating brass volume with more/less powder.

The reason I ask is because I only have so much brass and I have a match coming up requiring about 120 rounds. Of the 200 pieces of brass I have, if I split them based on one grain difference thats gives me only 62 pieces in the largest group.

 

[turbo54]

Re: Compensating brass volume with more/less powder.

At the risk of being an asshole:

1. Unless you are gods gift to shooting, you will have bigger issues than variances in brass weight during a 120 round match - like maintaining focus! I am f'n mentally exhausted after a 60 round 3x600 f class match.

2. Yes, in general heavier brass will show pressure sooner. For example, with a 175smk in IVI70 brass, a max charge in my rifle is 45gr. In Lapua brass, my goto load is 45.5, and max is over 46. Weight difference is more than 10gr for the brass.

3. My IVI70 brass has about a +/- 2.5gr variance, so a 5gr extreme spread. My rifle shoots it between 1/4 and 1/2 MOA....no weight sorting, and certainly no adjustments in charge weight. Extreme spreads of 15(ish)fps and 4-5fps standard deviation. Dont sweat it man. Focus more on shooting and less on loading!

4. I know it's easy to get into the nitty gritty in loading practices, but I promise you that YOU are the biggest factor! Leave the weight sorting/uniforming/meplat trimming/pointing etc etc etc to the benchrest guys, and FOCUS ON THE FUNDAMENTALS OF MARKSMANSHIP!!

 

[InTheWeeds]

Re: Compensating brass volume with more/less powder.

I hear ya man, but its tough when you have reloading OCD. I just want to take every other factor out of the equation if possible and know that the problem lies with the operator.

 

[turbo54]

Re: Compensating brass volume with more/less powder.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: In da weeds</div><div class="ubbcode-body">I hear ya man, but its tough when you have reading OCD. I just want to take every other factor out of the equation if possible and know that the problem lies with the operator. </div></div>

I know. I've been there. Ive played the sorting/neckturning etc etc game. Made me feel great going INTO the match, but the only thing thats made me feel good coming out of a match was practice like my life depended on each shot and supreme focus on the FoM (fundamentals of marksmanship).

 

[DocB]

Re: Compensating brass volume with more/less powder.

IDW,

The old Lapua reloading pamphlets used to say you could compensate by adding or subtracting 0.1gr of powder for every grain of case weight. Add for lighter cases, remove for heavier. They this could be used for up to 10 grains of case weight difference.

Caveats:

1. You probably won't be able to tell the difference.
2. Use this formula only within the same brand and lot of cases.
3. Test this before a match, not at a match.
4. Don't do this if you are showing pressure signs.

HTH,
DocB

 

[blklabs]

Re: Compensating brass volume with more/less powder.

Interesting that this thread comes up now. Last weekend I was shooting at CKA's and I tested out this theory on unfired win brass. I noticed during my loading that the majority of my brass the powder stopped at the base of the neck, on 20% of the brass the powder went halfway up the neck. I weighed the cases and there was weight variance of roughly 20 grains. I separated these two lots and used the same powder charge on each, 46.4 gr of RL17 with 208 AMAX.

While we were shooting, ChadTRG brought out his chrono and the heavier cases (less internal volume) were 60fps faster than the normal cases. When we bumped back to the 1k tower, I had .6 mils of vertical difference between the two batches of brass or 21.6" of vertical.

During my load development this load was 13es, 5sd. Monday I called Winchester and they said to send in the brass and they would QA them and give me replacement brass.

Long story short, I would definitely test your loads and see what the velocity differences are between the 5gr spreads and then plan accordingly. Good luck!