Xtp hollow point vs. Xtp flat point consistency differences in .357 magnum

[Big-bore-bob]

Hello all,
Had a testing session this weekend with several loads for my .44 mag and .357 magnum smith's. For the .357 686+, 4 inch barrel, using 158gr xtp hp's and fp's over 15.5gr h110, cci 550, coal 1.575, starline brass, I recorded a large difference in SD and ES between the two bullet types. Xtp hp: SD 11, ES 38, avg vel 1245, hi of 1259, lo of 1221. Xtp fp: SD 28, ES 88, avg vel 1224, hi of 1265, lo of 1177. In my hornady manual both bullets are listed under the same load data. When I measured the base of the bullets to the bottom of the cannelure the FP is shorter than the HP ( less bullet in the case for the FP). Do to local availability I've been buying both style of bullets. My question is: what would cause the difference in performance between the two bullets? ( larger case volume with the FP) Would increasing powder charge with the FP possibly stabilize the h110 powder burn? I belive 15.8 is the max load per hornady. Anyone see these sort of results before? .357 is my newest cartridge I'm reloading/ handloading for. Thanks!

 

[BBarn]

What were your sample sizes?

 

[Big-bore-bob]

What were your sample sizes?

I chrono'd 20 rounds of each type, randomly pulled from 100 round batches. I loaded all 200 rounds in the same session, 100 hp's, 100 fp's.

 

[ArchAngelCD]

I really don't see a big difference between both bullets. There are too many other variants to guess why the SD/ES numbers are different. Of course case space is one of them but exact powder charge and more are also involved.

The data you quoted from Hornady is quite different than the data Hodgdon published. The Hodgdon data is quite a bit higher.

 

[Big-bore-bob]

The Hodgdon data is quite a bit higher.

Sorry, hornady lists 15.6 as max, lyman max is 17, nosler max is 15.6. I didn't check hodgdon. In my original work up I went as high as 16.5 but I had gas leakage around a few of the primers and some cratering of the primer indents so I backed off to 15.5. Could a few loose primer pockets have caused that primer blow-by? That was my cue to back off the charge weight but I'm not as experienced as you all.

 

[ArchAngelCD]

I'm not sure why and if you are getting gas leakage around your primer but I find it hard to believe it's the charge weight.

I have personally load many hundreds of 158gr XTP bullets over 16.7gr W296/H110 without a problem.

Is it possible for you to post a few pictures of what you are seeing. Primers are not a reliable source for reading pressures.

 

[Big-bore-bob]

Unfortunately I already threw out the suspect cases only a few of them had leakage around the primer and i noticed a few primers seat way to easily during the initial loading (brass was new starline) i assumed, perhaps incorrectly, these were the leaky primer rounds. Are some raised edges around the primer indent normal? Based on your charge weight of 16.7, can I deduce my inconsistencies may be another h110 problem? Perhaps not enough case fill causing ignition/burn inconsistencies? I believe I had the same issue working with H110 in my 44. In the future I will more diligently record my data to include pictures of anomalies.

 

[AJC1]

Unfortunately I already threw out the suspect cases only a few of them had leakage around the primer and i noticed a few primers seat way to easily during the initial loading (brass was new starline) i assumed, perhaps incorrectly, these were the leaky primer rounds. Are some raised edges around the primer indent normal? Based on your charge weight of 16.7, can I deduce my inconsistencies may be another h110 problem? Perhaps not enough case fill causing ignition/burn inconsistencies? I believe I had the same issue working with H110 in my 44. In the future I will more diligently record my data to include pictures of anomalies.

We're not exactly forensic scientists, but being able to see all there is to see helps in problem solving. What brand of primers were you using? If I shoot a ladder and something comes up I shoot a picture of the test box for later analysis.

 

[Englishmn]

Highly likely that the case capacity difference is the cause. Seat a few fp deeper so base is same position as hp bullet and results should be the same. In my experience h110 liked being closer to max.

 

[Big-bore-bob]

What brand of primers were you using?

Cci 550 magnum.

 

[Big-bore-bob]

Seat a few fp deeper so base is same position as hp bullet and results should be the same

I would do this, however the cannelure is in the same position on both bullets so too deep and I can't roll crimp into the groove.

 

[AJC1]

I would do this, however the cannelure is in the same position on both bullets so too deep and I can't roll crimp into the groove.

If the seating depth is that different then treat them as two different loadings. Download Gordon's reloading tool and compare them for pressure

 

[Big-bore-bob]

treat them as two different loadings.

This I can do... I think ill work up my charge weight a bit more with both bullets, then take the FP a little further than the HP and see what sort of results I get. (Looking for pressure signs and being more detailed in my data records) I'll be sure to take pictures this time for referencing incase I run into a similar problem in the future. What exact details you all include in your range notes when testing new loads?

 

[eddiememphis]

Are you measuring the powder in each load by hand or using a powder measure?

 

[AJC1]

This I can do... I think ill work up my charge weight a bit more with both bullets, then take the FP a little further than the HP and see what sort of results I get. (Looking for pressure signs and being more detailed in my data records) I'll be sure to take pictures this time for referencing incase I run into a similar problem in the future. What exact details you all include in your range notes when testing new loads?

Bullet, primer, powder launch platform, temperature and wind. I put cases back in the load box in test order to compare primers. That covers most, if I bring a crono, most times I don't that data as well. The easiest way to get weather data is a screen grab off your phone. It's very warm so I consider loads currently operating in the top of their range.

 

[Big-bore-bob]

Are you measuring the powder in each load by hand or using a powder measure?

I'm using rcbs uniflow competition pistol powder measure. I've gotten very consistent results with this powder measure using H110, hp38, bullseye, and cfe pistol, in .45 acp, .357, and 44 mag. I use rcbs check weights with my lyman accu-touch digital scale to verify charge weight accuracy.