505 Gibbs, H4831

[ACraig]

Just returned from a range session with my 505 Gibbs, and I'm a little baffled and wondered if anyone else has experience that could be of help. I loaded 5 of the 525gr TSX with 117gr - 129gr of H4831 powder. Also loaded 5 of the CEB 525gr solids with 117gr - 129gr of H4831 powder.

Chrono Data - 525gr TSX H4831:
117gr - 1663fps
120gr - 1772fps
123gr - 1869fps
126gr - 1915fps
129gr - 1933fps

Chrono Data - 525gr CEB Solid H4831:
117gr - 1629fps
120gr - 1811fps
123gr - 1836fps
126gr - 1955fps
129gr - 1972fps

These readings seem much lower than I expected, and felt recoil seemed remarkably higher than these velocities would suggest. I'm suspicious that I'm not getting correct readings from my chronograph.... BUT, when I clocked some reduced loads, 600gr cast bullet over 50gr of 5744, it was spot on where it should be, 1483fps. Maybe I've got an extra slow batch of H4831, or maybe I should change powders. Helpful insight would be greatly appreciated.

Thank you!

 

[bruce moulds]

acraig,
I do not have a 505, which makes your post interesting.
nick harveys practical reloading manual 7th edition lists 525 gn bullet at 2260 fps using 132 gns ar2213sc.
ar2213sc is rebadged as h4831, possibly sc but not sure.
this load is listed as a starting load, but there is nothing under max.
similarly, 140 gns imr 7828 gives 2240, starting load only.
it also lists 133 gn re 22 as giving 2270, start, and 136 gn re22 as giving 2330, max.
sorry that is the best I can offer.
bruce.

 

[ACraig]

So far, it seems to me, two things are occurring. One, I've got a slow batch of H4831. Two, I've got a chronograph that's reading low. I've got a new chronograph on the way, that will definitely clear things up, I hope! Thank you for your input.

 

[postoak]

Where did you get your load data?

 

[ACraig]

Barnes lists RL22 with the 525 TSX, 125.5gr - 133gr, for a max velocity of 2223fps. I know there's not a direct substitution using powder burn rate charts, but H4831 looks to be very similar, if not a touch faster than RL22. Basing a theoretical max of 130gr (conservative) of H4831, reduce 10% and work up. So extrapolating Barnes data, 129gr of RL22 should produce ~2127fps; believable. Using the same bullet, case, primer, and then substituting a slightly faster powder, H4831, using 129gr gave me 1933fps, about 200fps slower than expected. But, a second chronograph will certainly clear things up.

 

[Rum Runner]

If it helps, I load for my .416 Rigby. Chronograph tested 400 a-frame, with 95 grains of H4831, 2323 fps (25 inch barrel on a CZ 550).

 

[ACraig]

Well, now I have two correct chronographs

I corroborated my original numbers with a new chronograph, and both are reading the same. I guess I've got more work to do!!

AC

 

[postoak]

Are you using magnum large rifle primers?

Have you fired and chronographed factory loads? What was the result?

Try some 4831sc maybe?

This is a good mystery! Don't just fade away on us!

 

[ACraig]

I've not fired factory loads in this, and at $15/pop, I doubt I will anytime soon. And yes, I'm using Large Rifle Magnum primers.

Interestingly, I've read some anecdotal evidence of "slow" .505's due to having oversized barrels, .507-.508". I haven't slugged the bore yet, but I may do that soon.

I've read direct accounts of people using H4831 at 130gr and reaching 2200fps+ with 525gr bullets. They indeed may be correct, or maybe they lack a chronograph. Regardless, in my rifle, 130gr gives 2000fps @ 10yds from the muzzle. Data extrapolation suggests that I'll reach my goal of 2150fps by using 140gr of H4831. I'll be loading those up soon.

I've got some new DGX Bonded bullets on the way for this rifle and my .375 H&H. I'll see how these react to H4831 as well.

I do not have a copy of the A-Square "Any Shot You Want", but apparently they have published data for H4831 under the 525gr bullet. If anyone has a copy, feel free to share. I'd be interested to see their results.

 

[Edge]

 

[ACraig]

Much obliged, good Sir!

 

[postoak]

Please let us know the result when you have the bore slugged. I would think a gunsmith could do this quickly and at little cost to you.

 

[ACraig]

The barrel slugged at .506 - .507".

 

[postoak]

Hmm, I'd be tempted to buy some .510 diameter bullets and order a custom bullet sizing die from Lee to size them down to .507.

https://leeprecision.com/custom-lube-and-size-kit/

https://leeprecision.com/bullet-casting/bullet-sizing-kit/

 

[ACraig]

Interestingly enough, as I was pushing the bullet down the bore, it became very easy once I neared the chamber, but still several inches up the barrel from the chamber. That tells me that where the bullet is initially engraving into the bore, it's fairly oversized. That's probably why this rifle appears "slow", as I'm getting a fair amount of escaping gas. I do shoot cast bullets, .507" 600gr gas checked, out of this rifle as well. I've got reduced loads of 5744 and full tilt 140gr of H4831. I haven't chrono'd the full tilt loads, but the reduced are spot on with other people's results. I'll post them here after my next range session.

Interestingly enough, IF it would chamber, and I don't know if it would in my rifle, but you could run .510" bullets in a .505 Gibbs all day long and it would do it quite safely. After reading some work that PO Ackley did on a modified rifle, shooting 8mm bullets out of a .30 cal barrel, bullet diameter, especially within a few thousandths, is the least of your worries.

 

[postoak]

So unmodified .510s should be okay if they will chamber and you work up to a safe load? I'd try that next.