IMR 4895, Weird Velocities, Seeking load data

[RetroJunkie98]

[VASCAR2]

[Lemonaid]

I'm just getting acquainted with Gorden's Reloading Tool (GRT). You might like to get a free download and explore what it has to offer. My beginner results from GRT puts a Grendel with IMR 4895 with 129 abler (len=1.350) with a case OAL of 2.280 max before warnings = 26.6 for a velocity of 2141 from a 12.5 barrel. (52782 p.s.i.). Disclaimer: The tool is just an estimate, I'm not advocating going past published load data, don't try at home etc....
There was one warning: low burn rate, inconsistent combustion, and increased error rate of the simulation very likely.

[Oso Polaris]

There is a difference between the H & I, most notably that IMR is temperature sensitive. But they are similar in burn rates. Here are a couple of threads comparing H4895 and IMR 4895, with both indicating that H4895 is faster than IMR4895, and usually a a few tenths more IMR powder will be needed to achieve the same velocity at the H4895 load. Based on this, you have a much larger delta in powder weights (as much as 1.6gr), which is the main contributor to the velocity difference.

https://forum.accurateshooter.com/threads/h-4895-imr-4895.3844184/

https://forum.accurateshooter.com/threads/imr-vs-h-4895.3744079/#post-35844038

Make it a science experiment: The only way to really know is to load a small batch using both powders at same charge weight while holding everything else exactly the same (new brass, primers from same sleeve, bullets from same box) and go shoot them side by side.

[JASmith]

There is a difference between the H & I, most notably that IMR is temperature sensitive. But they are similar in burn rates. Here are a couple of threads comparing H4895 and IMR 4895, with both indicating that H4895 is faster than IMR4895, and usually a a few tenths more IMR powder will be needed to achieve the same velocity at the H4895 load. Based on this, you have a much larger delta in powder weights (as much as 1.6gr), which is the main contributor to the velocity difference.

https://forum.accurateshooter.com/threads/h-4895-imr-4895.3844184/

https://forum.accurateshooter.com/threads/imr-vs-h-4895.3744079/#post-35844038

Make it a science experiment: The only way to really know is to load a small batch using both powders at same charge weight while holding everything else exactly the same (new brass, primers from same sleeve, bullets from same box) and go shoot them side by side.

+1. Go go for the experiment!

[RetroJunkie98]

[richj]

I loaded 120 Sierra HPBT and IMR 4895 to 27.5gr, no pressure signs. but no chrono setup. not the best groups.

this is in a 20" bolt gun. group opened up at 28gr.

[RetroJunkie98]

I loaded 120 Sierra HPBT and IMR 4895 to 27.5gr, no pressure signs. but no chrono setup. not the best groups.

this is in a 20" bolt gun. group opened up at 28gr.

Thanks for the info! Was the powder getting extra crunchy at that charge weight? I know my 130gr loads with h4895 are definitely compressing.

[tdbru]

RJ,
another difference between bullets of the same weight that does affect loading is: bearing length, jacket thickness and jacket hardness, lead core alloy composition which affects hardness. these variables influence the engraving resistance which influences which powder burn rate and amount is required. in the extremes, for example, a highly aerodynamic 100gr boat tail varmint bullet with thin jacket with a pure Pb core, having little bearing length will engrave into the rifling with less force than say a 100gr. flat base thick jacketed softpoint with a Pb and antimony alloy core with longer bearing length. so even with the same powder type and lot number, these two 100gr. bullets will have different load data for them. So it is not to hard to understand why bullet maker A's 100gr bullet has different load data for the same canister grade powder than bullet maker B's 100 gr. has. And then there's the variation with brass lot numbers, primer lot numbers, different pressure testing setups, etc. and though the differences may be small, when you have a lot of them they can add up. And what a reload data book reflects is just how all those variables for that manufacturer lined up on that given day when they were pressure testing loads for that specific cartridge with the specific components they used and the testing setup that they had and the test methodologies that they used to generate the data that went into their reloading manual.
Get a look at as many reload manuals as you can and cross reference. The more knowledge the better.
have fun. be safe.
-tdbru

[RetroJunkie98]

OBLIGATORY: I am not a reloading data source, this is not safe load data. Do not replicate these loads without following good procedure and working up to them. My data here is well and truly past any recorded max loads for these powders.

My test results are in! Today was 66*F, which is important for IMR 4895. For these I loaded 2 of each charge. Just in case the chrono got screwy as sun settled down this evening. Alas, all 10 registered! Rejoice!

Gun:
12.5" Faxon
Sandman Ti
H1 Buffer
Adjustable gas block and Gemtech suppressed carrier.

Loads:
Hornady brass
CCI 450
129gr ABLR
IMR 4895

Charge (gr) Velocity 1 Velocity 2
26.3 2051 2054 (ABOVE Nosler MAX LOAD)
26.5 2038 2070
26.7 2073 2051
26.9 2119 2086
27.1 2113 2119


There was absolutely 0 pressure signs on the brass. The primers were still nice and round. No ejector wipe. For comparison I'll drop my data for H4895. The temp for this test didn't matter. H4895 is so temp stable it's not worth recording. 1 shot per charge.

Charge (gr) Velocity
26.3 2143
26.5 2164
26.7 2192 (Hornady Listed Max)
26.9 2171
27.1 2207 (ABOVE MAX, ejector wipe and primer pocket loosening)
27.3 2207 (ABOVE MAX, ejector wipe and primer pocket loosening)