.45 ACP Carbine...what's the best ammo?

asdaven · Jul 5, 2021

Built a .45 ACP AR-15 with 16" barrel. Shot it the other weekend with standard 230 grain FMJ .45 ACP. I know its a pistol round. But im wondering if lighter grain ammo would fare better in a carbine?

Wanted to build another PCC AR and Picked .45 ACP cause I like the round. But was debating .40 S&W or 10mm. 10mm does not work well in a blowback cause it's too powerful and too long and im just not a fan of .40 S&W. But maybe shouldve gone with .40. I already have a 9mm and I can get decent groups at 100 yards with that with the right ammo.

But im wondering if I got some 185 grain or maybe even 165 grain if they make it in .45 ACP, that it would preform better at distance? Beyond 50 yards...the 230 grain rounds go all over the place it seems. Curious how lighter ball ammo performs. And if the lighter ammo would gain more velocity from a longer barrel?

TheOriginalMexicanBob · Jul 5, 2021

You can buy 185 grain .45 ACP if there's any available. Winchester Silvertip hand grenades are that weight. I say "hand grenades' because they're quite hot. You can also find 230 grain +P on the market sometimes. I had an Olympic Arms M4 in .45 ACP and it was quite accurate but I sold it. Overall you might just stay with 230 grain because it's the most easily found. A potential problem with the lighter weight bullets that are hollow point is the additional velocity may cause them to open up too quickly and limit penetration.

Harrys · Jul 5, 2021

Super 45s comes to mind

asdaven · Jul 5, 2021

TheOriginalMexicanBob said:
You can buy 185 grain .45 ACP if there's any available. Winchester Silvertip hand grenades are that weight. I say "hand grenades' because they're quite hot. You can also find 230 grain +P on the market sometimes. I had an Olympic Arms M4 in .45 ACP and it was quite accurate but I sold it. Overall you might just stay with 230 grain because it's the most easily found. A potential problem with the lighter weight bullets that are hollow point is the additional velocity may cause them to open up too quickly and limit penetration.

They make Flat Nose FMJ 185 grain rounds.

Pale Ryder · Jul 5, 2021

225-230 grain truncated cone bullets if you reload and they feed reliably. Someone I’m sure makes factory loads too.

TheOriginalMexicanBob · Jul 5, 2021

asdaven said:
They make Flat Nose FMJ 185 grain rounds.

There's also 185 grain target wadcutters but I wouldn't recommend them for anything other than bullseye use...too mild for anything else.

Biggfoot44 · Jul 5, 2021

Whatever is most accurate in your gun .

Unlike 9mm or .357 etc carbines , .45acp from a 16 inch has minimal velocity gain over a 5 or 6 inch bbl , maybe +/- 100 fps . With low pressures and very high expansion ratio , that's just the facts of life of physics and chemical engineering .

Not inherently a slam on .45acp carbines , if you like .45acp ( or want a companion piece , you still get all the ergonomic advantages of a shoulder gun , but your trajectory won't be meaningfully flatter than a 1911 .

lazarus · Jul 6, 2021

Harrys said:
Super 45s comes to mind

You'd almost certainly want a delayed blow back gun for that. That's one of the problems with 45 PCCs, unless based on a delayed blow back action, you are stuck with standard pressure 45. Maybe you might push it for +p. The amount of weight and strength of spring you'd need to safely and reliably run 45 super without beating up the gun is very, very significant.

OP, if your 230gr ball is going all over the place at 50yds, that's either an ammo issue, a gun issue or a shooter issue. The amount of wind drift on a 230gr .45acp at 50yds unless it a tornado is minimal. 100yds it could be noticeable and beyond certainly can end up scattering it all over the place.

However, a 185gr is going to slow down a lot faster than a 230gr, even if it starts out a lot faster. 45 is just a big slow round and ballistic ally isn't that good. A 185gr is going to get pushed around more by the wind than a 230gr would.

Best bet is, unfortunately with todays prices, try several different ammo types from different manufacturers to see what the result is.

The other issue is that most RANGE ammo is not going to be made with particularly tight tolerances and is aimed at users who are shooting a pistol off hand at perhaps as much as 25yds who are probably only going to care about coffee can accuracy at those distances.

Unfortunately you'll likely need to either reload, or track down high quality ammo if you want much better than about 10MOA IMHO.

lazarus · Jul 6, 2021

Biggfoot44 said:
Whatever is most accurate in your gun .

Unlike 9mm or .357 etc carbines , .45acp from a 16 inch has minimal velocity gain over a 5 or 6 inch bbl , maybe +/- 100 fps . With low pressures and very high expansion ratio , that's just the facts of life of physics and chemical engineering .

Not inherently a slam on .45acp carbines , if you like .45acp ( or want a companion piece , you still get all the ergonomic advantages of a shoulder gun , but your trajectory won't be meaningfully flatter than a 1911 .

I'd really like a delayed blow back PCC in 45 super (that'll also run with standard pressure 45). Load up some 250/260gr 1050fps out of a 16" for some fun subsonic suppressor loads (might even be able to load some 300gr to 1000fps). Run some really hot 185gr loads at 1600+fps.

Plink with some 950fps 230gr.

PS 45 super gains a whole lot more with a longer barrel because of that higher pressure. 45acp gains maybe 100fps going from 5" to 16", maybe 150fps for a 185gr +p round. 45 super though can tack on another 200fps with 230gr from 5" to 16" and lighter weight rounds its more like 250fps.

asdaven · Jul 6, 2021

lazarus said:
You'd almost certainly want a delayed blow back gun for that. That's one of the problems with 45 PCCs, unless based on a delayed blow back action, you are stuck with standard pressure 45. Maybe you might push it for +p. The amount of weight and strength of spring you'd need to safely and reliably run 45 super without beating up the gun is very, very significant.

OP, if your 230gr ball is going all over the place at 50yds, that's either an ammo issue, a gun issue or a shooter issue. The amount of wind drift on a 230gr .45acp at 50yds unless it a tornado is minimal. 100yds it could be noticeable and beyond certainly can end up scattering it all over the place.

However, a 185gr is going to slow down a lot faster than a 230gr, even if it starts out a lot faster. 45 is just a big slow round and ballistic ally isn't that good. A 185gr is going to get pushed around more by the wind than a 230gr would.

Best bet is, unfortunately with todays prices, try several different ammo types from different manufacturers to see what the result is.

The other issue is that most RANGE ammo is not going to be made with particularly tight tolerances and is aimed at users who are shooting a pistol off hand at perhaps as much as 25yds who are probably only going to care about coffee can accuracy at those distances.

Unfortunately you'll likely need to either reload, or track down high quality ammo if you want much better than about 10MOA IMHO.

It shoots fine at 50 yards. But I say that's the limit before I start getting fliers. 9mm with +P ammo in a 16" carbine I get an 1.5-2" group at 100 yards with the right ammo. .45 at 100 yards is all over the target. Yes maybe the 185 grain might slow down more. But thinking 185 grain .45 might act more like a .40 S&W round. What you said but at the same time less drop at distance than 230 grain. 185 grain still pretty heavy bullet to not get blown around I think. There was no wind when I was shooting.

alucard0822 · Jul 6, 2021

I've found bullet shape matters a lot for longer range 45, anything truncated cone HP, like XTPs or HAP will hold groups out at 100 and further, RN starts to open up. 185s can be OK or not, they will probably drop transonic somewhere down range, and some barrels like them, some don't. Would also be curious what buffer you are running, or if you have a chrony to shoot over. In blowback, some loads, especially low pressure loads can leak a fair ammount of gas, and can cycle a bit goofy, heavier buffers(10oz+) and hotter loads can often reduce the SD velocity spread and close up groups.

KIBarrister · Jul 6, 2021

My UMP (45 w/ 16" bbl) does enjoy 45 Super for accuracy. I'd imagine if my plastic H&K can handle the added pressure so too could your AR pattern rifle. In normal times I'd say buy a few boxes and sit with a chronograph and compare results, but finding a decent selection without breaking the bank right now is difficult. If you want something fast, underwood may be worth a box to see how it goes - it gets over 1,400 FPS, but it's pricey.

alucard0822 · Jul 6, 2021

KIBarrister said:
My UMP (45 w/ 16" bbl) does enjoy 45 Super for accuracy. I'd imagine if my plastic H&K can handle the added pressure so too could your AR pattern rifle. In normal times I'd say buy a few boxes and sit with a chronograph and compare results, but finding a decent selection without breaking the bank right now is difficult. If you want something fast, underwood may be worth a box to see how it goes - it gets over 1,400 FPS, but it's pricey.

Delayed blowback and blowback are 2 different things. HK's roller delay increases the range of pressures that the system can handle, as the rollers lock to hold the bolt closed till the bullet leaves the barrel and pressure drops. It is timed primarily through the engagement duration of the rollers. In blowback, the brass case is the lock, held in the chamber from pressure only, soon as pressure drops, it can slide out of the chamber and "blow back" against the bolt/buffer weight to cycle, works great in a relatively narrow pressure window. it's timed by case friction in the chamber and bolt/buffer mass. 45 supers or hot 10mm is fine with rollers or a delay mechanism to support the case while under max pressure, but blowback can have issues if a case separates or the bolt mass isn't enough to keep a safe bolt velocity with hotter ammo.

asdaven · Jul 6, 2021

alucard0822 said:
Delayed blowback and blowback are 2 different things. HK's roller delay increases the range of pressures that the system can handle, as the rollers lock to hold the bolt closed till the bullet leaves the barrel and pressure drops. It is timed primarily through the engagement duration of the rollers. In blowback, the brass case is the lock, held in the chamber from pressure only, soon as pressure drops, it can slide out of the chamber and "blow back" against the bolt/buffer weight to cycle, works great in a relatively narrow pressure window. it's timed by case friction in the chamber and bolt/buffer mass. 45 supers or hot 10mm is fine with rollers or a delay mechanism to support the case while under max pressure, but blowback can have issues if a case separates or the bolt mass isn't enough to keep a safe bolt velocity with hotter ammo.

I dont think I would run a .45 super in my blowback carbine. I am running a 10 oz buffer and a Tubb .308 spring plus a Wolf XP Hammer Spring plus of course a weighted .45 bolt. For my 9mm, I run the same everything except an 8 oz buffer instead.. Since it's not delayed blowback, this is about everything you can do to slow down the opening of the bolt. Plus I think it reduces recoil. Wondering if I could even get away with a 10 oz buffer in the 9mm because it throws brass a mile away. The .45 drops brass right next to me. Of course a .45 acp casing is a lot heavier than a 9mm casing. These setups both run good. Only hangups I've had were ammo and magazine related issues. Brass looks good. .45 ACP is a lower pressure round good for blowback over say a 10mm. Would really like a 10mm but that's why I built a .45 acp instead.

However, I think normal +P ammo is fine in 9mm or .45. I run mostly NATO loads in my 9mm. Seems to be the sweet spot. Would not run +P+ though. Unfortunately in .45, there is not a lot of +P offerings compared to 9mm that has many Nato and +P loads. But I think normal +P would be alright in my .45. But this comes back to the 185 grain loads. I would think this would shoot more like a .40 S&W and have similar ballistics which has less drop than a .45 ACP.

KIBarrister · Jul 6, 2021

alucard0822 said:
Delayed blowback and blowback are 2 different things. HK's roller delay increases the range of pressures that the system can handle, as the rollers lock to hold the bolt closed till the bullet leaves the barrel and pressure drops. It is timed primarily through the engagement duration of the rollers. In blowback, the brass case is the lock, held in the chamber from pressure only, soon as pressure drops, it can slide out of the chamber and "blow back" against the bolt/buffer weight to cycle, works great in a relatively narrow pressure window. it's timed by case friction in the chamber and bolt/buffer mass. 45 supers or hot 10mm is fine with rollers or a delay mechanism to support the case while under max pressure, but blowback can have issues if a case separates or the bolt mass isn't enough to keep a safe bolt velocity with hotter ammo.

The UMP is not roller delayed. It just uses a hefty bolt - and the manual from HK specifically green lights use of 45 super.

.45 ACP Carbine...what's the best ammo?

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