H4831SC Temp sensitivity / 6.5 PRC observation

[jesco88]

I'm just curious if anyone else has used H4831SC in a 6.5 PRC and shot in different temps and days...
Over a 20-round group, I was averaging around 2855fps from a 20" 6.5 PRC Seekins with a 143gr ELDX and CCI200 Primers in Hornady Brass. This was done back in April, ambient was around 40F.

I just got back from another 20-round session and velocity is up at 2875fps. Ambient was only 65F. But it was enough to give me a few rounds where I noticed the bolt lift was heavier than I expected. Its really hard to tell pressure signs, because of the dual ejectors on the PH3 bolt, but I did a 1 round ladder in powder charge, got all the way up to 2930fps before things got way, way too hot for my liking. I'm going to be dropping powder charge on the next batch I load anyways because I'm switching from CCI 200 primers to Fed 210M primers, and with my testing with a 6.5 Creed, the 210m primers gained an additional 20fps over the CCI200. Not sure how much that will translate with a 6.5 PRC, but nonetheless, with the occasional heavy bolt lift I was getting... I'm thinking I need to drop down anyways.

Its just odd, I didn't really expect to see that much of a difference between 40F and 65F... Especially with a powder that is known to be pretty decent with regards to temperature senstivity. Is there anything else I might be overlooking here? Perhaps the gun is somehow too dirty and messing with headspace or something? I only shoot this one suppressed, and I've heard others say that can affect pressure by carbon getting in the chamber or something like that? Idk...

 

[dreamingWest]

What chrono?
20 fps represents less than 1% difference at these velos. That wouldn't surprise me at all. I use a ProChrono and I'd be questioning exact lighting conditions and chronograph accuracy before thinking about temp sensitivity for H4831sc. Honestly, I wouldn't give a 20 fps delta even a second thought testing on different days.

I have used H4831sc in my 20" 6.5 PRC, but I only have data from one day of shooting.

 

[jesco88]

What chrono?
20 fps represents less than 1% difference at these velos. That wouldn't surprise me at all. I use a ProChrono and I'd be questioning exact lighting conditions and chronograph accuracy before thinking about temp sensitivity for H4831sc. Honestly, I wouldn't give a 20 fps delta even a second thought testing on different days.

I have used H4831sc in my 20" 6.5 PRC, but I only have data from one day of shooting.

Athlon Rangecraft. Never seen an issue with these types, if they're off, they're consistently off. I think its reporting 10fps high or maybe my BC is off with my 175smk blems... But out to 550yds with a 308... its within a tenth of a mil of exactly where I'd expect impacts to be.

For reference, same conditions with a 6.5CM using H4350- Nothing really different at all between the 40F day and the 65F day. I was 2653 with a 10 shot avg on the 40F day near the end of April, and 2655 today, 65F. I'm sure if I shot another 10round string, it might be 2654 or 2656... No biggie.

The 6.5 PRC SD was 8.8 over one 10 shot string, and a 26fps ES. So its not like its all over the place, fairly consistent. (1-10rd, and 2-5rd strings) the average was 2875.

Just one of those scratching my head moments trying to figure out why is it 20fps higher.....

*EDIT* NVM- I just realized I had seated those primers .001" below flush before at 2855fps. Got a few light strikes, went back and seated them 0.004" below flush when I had the right tool to seat them deeper into the case. God, it sucks getting old.

 

[bigunit]

Is your barrel fully broken in yet? They can speed up some up to 200 rounds.

 

[jesco88]

Is your barrel fully broken in yet? They can speed up some up to 200 rounds.

I'm probably right at about 100 rounds now. But I think I answered my own mystery. I was using a RCBS hand prime tool, and could only get the primers 0.001" below flush, or just at flush with the rim of the case. I shot 20+ rounds and had a few light strikes. Figured it was the 'ol Seekins special, only to question everything I was doing and checked the primer depths. Had to order a different primer tool to seat those primers deeper into the case, ended up at about 0.004" below flush, which is probably why I'm seeing a difference in velocity now. I haven't ever tested primer seating depth with regards to velocity. I don't think I ever will, lol. But I can only assume that with a proper seating depth, I'm getting a better flame than I was getting before, which is enough to let me assume that's why the velocity is higher.