Bullet de-stabilization

I have a ruger 77/357 with a 20" barrel that I am shooting suppressed. I worked up a load shooting a cast performance 200 grain bullet at about 1060fps (I did run it over a chronograph). 1:16" twist. I do not know the BC, but the bullet is .848 in long. At 100 yards, there is no key-holing evident, and I am shooting right at 1" groups. At 150 yards, I can still hit what I am aiming at. At 200 yards, I can't hit a 12 inch square plate. I am guessing that the bullet is de-stabilizing somewhere between 150 and 200 yards. Can anyone smarter than me confirm my suspicions? I am thinking I need to step down to a 180 grain bullet. What says the THF braintrust?

180gr bullets have worked in the 3 Marlin 357 Mag I have owned. I never went above that weight, never really saw the need to.

If zeroed at 100 you’re going to be roughly 35 inches low at 200. I would also look to 180s with a bit more pep.

This question is much easier to answer empirically. Put out a much larger paper target and see if the bullets are going through sideways at 200 yards to indicate tumbling.

Compared with the shape of the bullet holes, accuracy is a very difficult metric to use as an indicator of stability.

I could load the 200 gr with a bit more pep if I wanted to, but the idea behind this load is to be subsonic through a suppressor.

A subsonic 200 grain .357 doesn't have the steam to reliably use at 200 yards.

Good to see you post something outside of one of your own threads!
I had already thought of doing that, but won't be able to do that until the next trip down to the Ranch. I know that some guys here use a calculator to figure stability of a bullet before they even attempt to load it, and maybe can tell me how stable/ unstable that combo might be.

You may be right, but a lot of people say the same thing about a 22 at 300 yards.

I forgot to add that the velocity is still decent at 925 ish at 200 yards.

Im out of my own on this, but just a thought... At long range bullets loose stability when they loose to much velocity... right?

925 fps doesnt seem to me like it should be loosing too much velocity to be stable.

I think it’s (tumbling) usually caused by the bullet going transonic vs. a loss in velocity. At 300 yards my .22 rounds have dropped to 718 FPS and no tumbling has occurred (that I know of). What is the twist rate, it’s possible a really slow twist might cause this.

1in 16" twist. As it starts subsonic, it can't go transonic.

Also when I plugged that into the calculator I made up a BC. Anyone want to guess at it I may get it closer.

I have the same rifle and cut off 6" of barrel. It still stabilizes 247gr cast bullets well. I have plinked with them at longer distances and them seem to remain stable. Using a MV of 1050 fps. The 16" twist should be more than enough for a 200gr bullet.

I didn’t mean to imply it was going transonic, just that that’s normally what causes destabilization. I did miss the twist rate though.

Maybe I just need to figure the correct bc so that I can calculate the correct drop. Unfortunately, the manufacturer website does not list bc, so I am just taking an uneducated guess.

That's probably why the math says the velo is still "high" at 200 yards. I bet it's not almost 1K FPS. It's takes a pretty fat nose to get 200 grains out of a .357 bullet. I have a NOE mold that produces bullets that once GC'd and PC'd weighs 187-ish and it has a WIDE meplat and a flat nose.

Figure at least 1.2 mil of drop for every 25 yards and you will be in the neighborhood. Takes a lot of elevation to get those out past 200 yards.

Can you expand more on the 247gr loads? I SBR'ed my 77/357 and haven't had time to start loading, Where are you getting the heavy bullets? Powder? 50 & 100 yd accuracy? I assume you are shooting suppressed? Killed anything with it?
Thanks

Can you expand more on the 247gr loads? I SBR'ed my 77/357 and haven't had time to start loading, Where are you getting the heavy bullets? Powder? 50 & 100 yd accuracy? I assume you are shooting suppressed? Killed anything with it?
Thanks

Jhills. What are you shooting out of your 77/357? Here's the loads that I'm talking about in this thread.

Remington mag primer, 4.8 gr of Unique, and about 1 moa accuracy at 100 yards. As stated, I'm having all kinds of issues at 200 yards.
I haven't had the chance to kill any pigs with it yet. But that'll change this summer.

Mine is a 10" SBR, killed more stuff than the plague. 247gr cast at 1050fps. 5.0gr of HP38 does well.

Does your's cycle those monsters well? Mine will hang up on the 200 grain bullets occasionally. I have to cycle them with "gusto" in order to get 100% reliability.

I have not shot anything yet. I cut mine to 10 or 11" would have to check. About the time I did it the covid crap hit. Have been more focused on loading 6.8 for hogs.

Are you concerned shooting gas checks through your suppressor? You casting your own bullets (that looks like a Beartooth bullet)? Or buying from where?
I saw a guy loading 246's and even had some 300 gr on AR15 but not sure where he was buying. He said Federal brass 38 SPL cases worked best, Remington 38's were a no go. Would have to go back and reread to see what the issue was but the heavy bullets worked best with 38SPL brass.

Don't have H38 but have Unique and a few others.

Jhills, I had you and Glocker mixed up for a minute. I want to know if Glocker can cycle those monster bullets reliably. The 200 grain ones tend to hang up sometimes.

But, no, I am not concerned about shooting the gas checks through the suppressor. I guess one may have concerns with it falling off and having a baffle strike, but I have probably put 500 rounds through it already and have not had issue. I get the bullets from Cast Performance. I've got a TON of them if you need some. In winchester brass, I do not have any issues loading them in 357. Never had to use 38.

My cycled them well, using 357 brass. They are pretty good on hogs, never had one walk it off! Deep penetration, gun is very quiet but impact of the full wadcutter is quite loud.

That short barrel is sweet. I left mine at 20".

I wrote some of those stability calculators. The ones I've written (and most others) compute gyroscopic stability, which is lowest when the bullet leaves the barrel and INCREASES as the bullet flies down range. If a bullet is stable out to 150 yards, but not at 200 yards, the issue is dynamic stability which is much harder to predict with a simple formula. It requires knowing a bunch of coefficients about the bullet that are not generally available, and it is also much more strongly affected by manufacturing imperfections. The gyroscopic stability calculators also suggest your bullet has no problem with gyroscopic stability. If there is a stability problem, it is a dynamic stability issue.



All guessing at BCs can do is suggest a range of possible 200 yards drops if sighted in at 100 yards. I've also seen bullet BCs vary widely depending on the gun they are shot from as well as the velocity. Once bullet flight times are longer than about 0.5 seconds, the easiest approach to sighting them in is a really big target so your first shot is somewhere on the paper. Using a dirt backstop and a second person sighting can also be effective if they can see the hits and walk you in.

BC will vary slightly from barrel to barrel but not enough to really see at normal distances, maybe ELR stuff. Many bullets do better at subsonic speed. Either way, with subs 1.2 mil every 25 yards is going to be pretty close in most cases.

the "guessing" at BC, in my thread above came from NOE bullet molds who give the BC for their bullet molds. Their 197gr bullet mold without gascheck is very close to the one pictured with a slightly more pointed profile so I dropped the BC a little for the slightly larger meplat.

I know the Berger twist rate calculator is better for boat tail bullets and they give twist rate recommendations for their flat based bullets for that reason. .

Update to thread: I realized this weekend that my issues with stability was a tree branch at about 150 yards. Once I figured that out, I was able to cleanly hit the 200 yard target every time. Roughly 17 moa of drop at that range. I've also decided that the 200 gr load at approx 1020 FPS is not a reliable pig killer. I am sure that they are dead or dying, but I only recovered 2 of the four that I shot, and one of the recovered pigs I did have to track quite a ways. Not as quiet, and not as fun, but I'll go back to 158 gr at 1800 fps for hunting.

Another update to this thread, as I now have a torn up baffle. J Hills, you were right. Yes, you should be concerned shooting gas checks through a suppressor. David and I have decided that the gas check has probably been falling off and striking the baffle. UGH.