Is a "normal" slide sized blowback 45 ACP handgun feasible??


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saturno_v
March 3, 2010, 01:04 PM
The 25 ACP, 32 ACP, 380 ACP and 45 ACP are all creatures of John Browning, they were developed in the first decade of the 20th century (the 25 ACP in 1899)


All these chamberings share a somehow similar pressure profile (between 20.500 for the 32 ACP and 25.000 PSI for the 25 ACP)

They look like increasing scaled up version of each other.

We all know that up to the 380 ACP, the blowback design can perfectly handle these cartridges (the small Walther PPK is the most famous example of a small blowback 380 pistol)

My question is: Would it be possible to build a reasonably sized (let's say a bit smaller and lighter than a 1911) economical blowback 45 ACP pistol??

The round seems low pressure enough that a "regular" slide size blowback system (not something like a Hi-Point) should be able to handle it.

Any thoughts or opinion? Am I missing some technical detail?

Regards

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Echo9
March 3, 2010, 01:09 PM
As far as I know, it's possible, but you'd need a ridiculously heavy recoil spring.

Or a normal sized but quite heavy slide.

w_houle
March 3, 2010, 01:10 PM
As oppose to the brick of a slide on a Hi Point? You could do it, but what you shave off from the slide will have to be made up in added recoil spring tension. It could be done, but I wouldn't want to shoot it.:what:

NG VI
March 3, 2010, 01:15 PM
The pressures might be the same, but that isn't what dictates the type of operating system, the momentum is.

A .45 ACP has so much more momentum than the other three cartridges that it would take a bitchin' heavy recoil spring and a slide that somehow had some extra weight put into it, or it would take an ungodly heavy recoil spring with a normal weight slide.

Locked breech is so much better.

rcmodel
March 3, 2010, 01:16 PM
No, a regular size slide is not heavy enough.

There is more to pressure then just pressure.

When you move up the scale in bullet weight from 50, 71, and 90 grain bullets to a 230 one weighing 3 to 5 times more, recoil impulse and case head thrust becomes more then a blow-back of normal size can begin to handle.

It has been done on retarded blow-backs on some obscure designs like the Thomas .45 ACP but was never very successful.

Successful blow-back .45 ACP's have slides that look like the Hi-Point and weigh the same.

rc

saturno_v
March 3, 2010, 01:18 PM
Echo and w_houle


I see your point guys but up to the 380 ACP, the small Walther PPK can handle it perfectly...it can even take overpressure 380 Auto rounds.

The 45 ACP is obviously more powerful but, at least it seems to me, the power difference is not that much that a bit bigger slide and a bit stiffer recoil spring could not take care of it...maybe I'm wrong...

saturno_v
March 3, 2010, 01:19 PM
Thanks for claify that rcmodel!!

rattletrap1970
March 3, 2010, 01:29 PM
What about using a fluid to dampen the recoil ? Like a non-newtonian liquid?

rcmodel
March 3, 2010, 01:31 PM
Then it would not be a blow-back like the OP asked about.

It would be a retarded blow-back like I mentioned in post #5.

rc

NMGonzo
March 3, 2010, 07:27 PM
What is wrong with the current system?

Full Metal Jacket
March 3, 2010, 07:29 PM
AMT tried it in a compact model. it was uncontrollable, and a miserable failure on the market.

http://www.highstandard.com/Guns/amt_45acpbackup.jpg

kragluver
March 3, 2010, 09:05 PM
In order to be controllable, I think it would start to resemble a SMG - wasn't the M3 grease gun a blow-back design?

VA27
March 3, 2010, 09:19 PM
Build your slide of depleted uranium and use the strongest spring you can find.

The AMT 45 BackUp I had was a locked breech just like the 1911.

The Lone Haranguer
March 3, 2010, 10:22 PM
Hi-Point .45 slides are so massive because, in part, of the metal used. It is less dense than steel, so more of it has to be used to achieve the necessary weight. Even in steel, a straight blowback .45 will still have to be very large; it will not be slim and trim like, for example, the 1911. It would probably somewhat resemble a larger version of the H&K VP70 ...

http://www.imfdb.org/images/thumb/0/03/HK_VP70Z_1890.jpg/350px-HK_VP70Z_1890.jpg

... which was not a hot seller.

gc70
March 3, 2010, 11:59 PM
Impulse momentum increases fairly rapidly with heavier bullets.

.380, 95 gr, 955 ft/sec
impulse 1.792 kg-m/sec

9mm, 124 gr, 1140 ft/sec
impulse 2.792 kg-m/sec

.45 ACP, 230 gr, 835 ft/sec
impulse 3.793 kg-m/sec

9mm and 9mm Largo were chambered in straight blowback guns (Astra 600 and 400 models, respectively) through the use of heavy recoil springs, although the slides were not oversized.

Moving from 9mm to .45 ACP is not as big a step as from .380 to 9mm. It would be challenging to use recoil springs very much heavier than in the Astras, so a heavier slide might (or probably would) be inevitable.

9mmepiphany
March 4, 2010, 03:03 PM
also remember that a stronger recoil spring will affect the dwell time needed for reliable feeding from the magazine

Jim Watson
March 4, 2010, 04:07 PM
Tanfoglio has a blowback system that runs at .38 Super ballistics. But it depends on special brass so if you opened it up to .45 it would not be a real .45 ACP.

makarovnik
March 5, 2010, 02:10 AM
I think it more important the slide is heavy as opposed to just large. Maybe tungsten or something would work but it would still be top/front heavy balance wise like a Hi-Point. Maybe some sort of delayed blowback would work.

outerlimit
March 5, 2010, 09:29 AM
AMT tried it in a compact model. it was uncontrollable, and a miserable failure on the market.

http://www.highstandard.com/Guns/amt_45acpbackup.jpg

Your post is a miserable failure because the AMT .45 Backup is not a blowback design, it is controllable, and it is still the most compact .45acp automatic in existence, smaller than even the Kahr PM45. In addition to that, it is now being reproduced by High Standard.

9mmepiphany
March 6, 2010, 02:20 PM
it is now being reproduced by High Standard.
i don't think that should be taken as a compliment

Full Metal Jacket
March 6, 2010, 03:46 PM
your post is a miserable failure because the AMT .45 Backup is not a blowback design, it is controllable, and it is still the most compact .45acp automatic in existence, smaller than even the Kahr PM45. In addition to that, it is now being reproduced by High Standard.


'Orly?


The straight blowback system is the standard type in .22 rimfire pistols where it has excelled. The normally accepted maximum for straight blowback actions is the .380 ACP. The Russians wanted a straight blowback type pistol similar to the Walther PP .380 for their post-WWII service pistol and in experiment they decided that the 9x18mm Makarov was as far as they could push the design and still retain a reasonable slide weight and spring force. To be sure there have been some blowback 9mms or even a .45 ACP, but those have had massive slides or springs that defy mere mortal men. Here I'm thinking [Charles Petty talking] of the old Astra 400 that was one of the most unpleasant 9s I've ever shot. You better eat your Wheaties, too, if you try to compress that spring. Another example is the AMT Backup in 45acp that also used the power of the mainspring against the hammer to help hold things down. There have been some other blowback 9mms and even a .45 or two that probably were better boat anchors.

AMT didn't go out of business because it was a huge success...

might want to think twice before making rude comments about things you know not about.

outerlimit
March 6, 2010, 04:30 PM
your post is a miserable failure because the AMT .45 Backup is not a blowback design, it is controllable, and it is still the most compact .45acp automatic in existence, smaller than even the Kahr PM45. In addition to that, it is now being reproduced by High Standard.


'Orly?



Quote:
The straight blowback system is the standard type in .22 rimfire pistols where it has excelled. The normally accepted maximum for straight blowback actions is the .380 ACP. The Russians wanted a straight blowback type pistol similar to the Walther PP .380 for their post-WWII service pistol and in experiment they decided that the 9x18mm Makarov was as far as they could push the design and still retain a reasonable slide weight and spring force. To be sure there have been some blowback 9mms or even a .45 ACP, but those have had massive slides or springs that defy mere mortal men. Here I'm thinking [Charles Petty talking] of the old Astra 400 that was one of the most unpleasant 9s I've ever shot. You better eat your Wheaties, too, if you try to compress that spring. Another example is the AMT Backup in 45acp that also used the power of the mainspring against the hammer to help hold things down. There have been some other blowback 9mms and even a .45 or two that probably were better boat anchors.

AMT didn't go out of business because it was a huge success...

might want to think twice before making rude comments about things you know not about.

I apologize for the rudeness of my original reply, but you are mistaken the AMT Backup .45 is in fact a locked breech design. And it appears that you're quoting a post from SKS boards as evidence to support your claim that it is a blowback design. The post is incorrect.

This can be cleared up quite easily,
http://www.youtube.com/watch?v=A1j0g0ccXU0

Above is a disassembly video for an AMT Backup in .45acp. You can very clearly see that it is a locked breech design, not a blowback. The AMT Backup in .380 is in fact a blowback design.

I never claimed that AMT was a huge success, but they were in business for quite awhile, sold a huge amount of guns and they are still in production by other firms and that was the only point I was trying to make. So calling the AMT backup series "a miserable failure on the market" is also factually incorrect. I never claimed they were (or are currently) high quality weapons, that High Standard is wonderful, or anything of the sort.

Magnumite
March 6, 2010, 04:42 PM
the Tommy gun is a blowback firearm with a slide made of steel. It is quite large and heavy. You can't change physics.

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