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Wondering "how low can I go" load-wise with an XP-100R factory ~14" barrel? Mostly for someone who is recoil sensitive and will be shooting from the flop position with a rifle scope. I found some info regarding the needed Terminal Momentum for Big Bore Rams, but not for the half scale critters. I think RP was running 55gr bullets at about 2200 fps muzzle velocity some time back. Not sure how that worked out in the long term.

New toy, that I hope I don't get to shoot TOO much, as I hope it gets taken over by another....Might even make it convertible between peep sights and scope.

I shoot 53g Noslers out of a 10" 221. Velocity is near what you are quoting and recoil is probably higher than you should get with 14" rear grip. No problem knocking over HS rams, topples >75% BB rams.

Good to know. I was shooting BB with a cobbled up manually operated AR pistol last year (2017) using heavy .223 bullets with no problems, except that the recoil from the heavier scoped gun cut Lisa's forehead a little. She's been a bit shy of them since, no surprise!
Hoping to configure the XP-100R to about the same as the flop Unlimited Anschutz which she's been running pretty well. (Last outing she hit everything she aimed at in SB, it's just that where she was aiming wasn't always the correct animal. Upgrade done in the front sight may help next year. Hoping to equip the XP-100 with similar sights as an option to a scope.)

If we can make this pistol with it's slow twist barrel work without adding a muzzle brake, that would be excellent!

You may want to consider a muzzle brake,and take the worry out of flinch or a black eye.
Brakes are not expensive,but the labor can be.Mike Dewey made the best ones,I haven’t talk to him in several years,at that time,he said he had a few left.
We’ve had a couple of the XP100R’s,in 223 at OKCGC running 55’s,with very few ringers,but it does happen!

Bullet construction is VERY important for small bullets hitting heavy targets. Super fragile soft points (and probably ballistic tips) "explode" when hitting steel and do not push enough energy or momentum into the target. Less frangible bullets are the key, including FMJ. If driven hard or fast on softer steel targets, they might cause damage. At slower speeds, like quoted above, there seems to be no target damage but high target reliability.

Watch your velocity ! I tried the exact thing that you are (factory XP 223), and gave up on it because the only loads that worked were near-max, and target damage was definitely a problem ! Also, the heaviest bullets that MY XP would handle accurately were 55 grainers. Good luck !

Too bad these things aren't as easy to rebarrel as an AR, or even a Savage. I have scads of heavy 0.224" bullets, but the rifling twist in the stock XP-100 barrel is not compatible. The 77gr bullets were working well on everything except for sloppy Ram hits out of the AR pistols in BB, but trying for a better flop configuration than is easily achieved using the evil black gun kluges.

Rebarreling isn't off the table, though, if it comes to that! But not for a while. Still putting this thing together.

Found some manual references to reduced 55gr loads using IMR4759 and AA5744, but they may not be ideal much past 100m. Getting into that wind sensitive trans sonic realm. Surely ought not recoil much, though!

IMR 4759 probably isn't an option. They quit making it a few years ago, and supply is limited to finding other shooters with a stash they no longer shoot.

aggshooter wrote:IMR 4759 probably isn't an option. They quit making it a few years ago, and supply is limited to finding other shooters with a stash they no longer shoot.

Bought quite a bit a year or two ago, New> Already had some, so there's enough for quite a bit of shooting! I does work well with the 7TCU cast bullet loads, however that one is very much NOT a flop pistol, which is what we're concentrating on currently.

ETA: more correctly SR4759.... ;)

I just bought a can of 5744, I plan to load some up and compare it to SR4759, but that project will have to wait for warmer weather. 4759 is a favorite of mine for a couple of silo pistols, but I still want to explore it for additional calibers
Sorry for the hijack...