300 blk case capacity testing

[Viking painter]

Hi all, I hope you’re all having a great weekend. Anyhow, I’ve been cleaning up and getting ready to load up some more 300 blk ammo and I thought I would do a case capacity test for using QL and GRT to develop loads for some new bullets I have. All cases are 1 fire, not resized, avg measurement was 1.356, some converted and some factory 300 blk. I did all the case capacity tests using h110 since it seems to be the closest to h2o tests that I’ve found and is much easier and more consistent than water imo. I tested 100 of each head stamp to get a good average on them. Here’s the results.
Factory 300 aac:
S&b= 24.7 gr
AAC= 24.8 gr
Hornady= 24.7 gr
GFL= 24.4 gr
LC 300 blk= 24.9gr
AP(armscor)= 24.4 gr

Converted .223/5.56 cases:
LC22= 24.9gr
RP= 25.1
PMC 223= 24.8
PSD(pmc xtac)= 24.9
AUSA(armscor 223)= 24.0

I will add numbers of these once they are resized and primed but thought this might be useful information to pass along. Like I said, I did 100 of each so large test samples to work with.

 

[FROGO207]

I am just starting on the 300 BLK reloading journey in the past few months. Have just been reloading plinking ammo so far. Thank you for taking the time. Never realized there was as great a spread to them.

 

[Viking painter]

I am just starting on the 300 BLK reloading journey in the past few months. Have just been reloading plinking ammo so far. Thank you for taking the time. Never realized there was as great a spread to them.

There is a big difference in headstamps. When I first loaded for 300 blk, I didn’t understand how the same load, same primer, same bullet and seating depth could have no pressure signs and shoot to expected velocity with one headstamps or factory blk cases then another would flatten primers and have ejector swipes really bad. I figured it out reading others experiences on this and other forums years ago and haven’t had any problems since. There’s a reason people prefer LC nato or RP converted cases and it is capacity and consistency. If you convert cases, stick with one that works for you, develop your loads with just that headstamps and you won’t get yourself into any trouble. I once had case heads rip right off and lucky I didn’t blow my gun up, scary stuff!! Be careful, start low and work up and keep everything consistent, and most of all have fun 300 blk is a fun cartridge to work with.

 

[Viking painter]

I tested a few more
LAX 300 blk= 24.4 gr
Lehigh 300 blk= 24.8
Winchester 223 converted= 25
Winchester 556 converted =24.9

 

[FROGO207]

Viking painter I also reload 223 and have for decades. The case volume of those when used did not change the accuracy or velocity to any appreciable amount for me. The 308 brass was a different story large differences in case capacity caused problems. I guess the smaller internal volume of the 300BLK round will have a bigger effect on things. There was a post previously about which 223 cases you could convert without neck turning and I think that this and the case volume numbers will be good guidance as to which ones I expend effort to convert.

 

[Viking painter]

Viking painter I also reload 223 and have for decades. The case volume of those when used did not change the accuracy or velocity to any appreciable amount for me. The 308 brass was a different story large differences in case capacity caused problems. I guess the smaller internal volume of the 300BLK round will have a bigger effect on things. There was a post previously about which 223 cases you could convert without neck turning and I think that this and the case volume numbers will be good guidance as to which ones I expend effort to convert.

Yes, 223/556 is not as sensitive to case volume but a little.As you said, the small case of 300 blk has a profound effect on pressure, the best to convert are LC NATO, LC 223, PSD(xtac), PMC, Winchester, and RP, if you have plenty of these headstamps I wouldn’t even convert any others. RP 223 are the best and most consistent commercial cases I’ve found to convert. Largest internal volume and consistent neck thickness. I fire form, shoot 1 more time then anneal and you should get 6-7 loadings or more.

 

[jmorris]

I am just starting on the 300 BLK reloading journey in the past few months. Have just been reloading plinking ammo so far. Thank you for taking the time. Never realized there was as great a spread to them.

You can also run into wall thickness issues on cut down .223 brass.

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