LCP barrel thickness

ragwd · July 10, 2013, 12:02 PM

Hello all, thanks for taking the time to read my thread and all replies are appreciated. I am not a smith or a engineer. I do have a nice set of calipers and I know how to read them and I am a bit curious. I love my LCP, I have at least 500 trouble free rounds down range with it. So the proof that the barrel works well is evident. I am just amazed at how thin a section of barrel is. Outside diameter is .378 at the narrowest point and the inside diameter is .352 and the difference is .026 that divided by 2 gives me a barrel wall thickness at the thinnest point is .013 , that is about the same thickness of a nice business card. Is there a reason that they made it so thin, besides cost, although it probably cost more to to machine that depression than to not and leave it the same diameter as rest of out side diameter. Obviously it will hold the pressure but why ??? Is it because the pressure is not a issue at that point in the barrel and they used the extra room created to reinforce the slide at that point ?? I am betting it is something obvious that a novice like me doesnt see. Those numbers are just eye opening. Sorry for the long winded thread I just felt it necessary to explain my question. Thank you.

James K · July 10, 2013, 12:49 PM

Because the slide is so short, that depression is necessary to allow the barrel to be removed when disassembling the pistol. I have no doubt that the Ruger engineers made sure there is still enough metal for safety.

Jim

ragwd · July 10, 2013, 01:55 PM

James, thanks , and the fact that ive run so many down range proves that. but the fact that it is only .013 inches thick just says WOW to me.

GJSchulze · July 10, 2013, 02:24 PM

By the time the bullet passes the thin spot, the pressure has dropped a lot. Before it passes that spot, there is no (additional) pressure. But, wow, that is thin!

CowTowner · July 11, 2013, 07:31 AM

The barrel on a Kel-Tec P3-AT is of the same design for the same reason James K mentioned.

GJSchulze · July 11, 2013, 01:58 PM

And yet my XD 9mm subcompact barrel (3") has no such depression and looks to have thicker walls. I guess every design has tradeoffs.

Dixie Gunsmithing · July 11, 2013, 02:09 PM

Actually, the other reason for the 'knobbed end', as I've heard them called, serves the same purpose as a ball joint. When firing, with a cylindrically round front barrel busing or bearing surface, the barrel's rear end has to drop down to unlock, so in order for it to move this way, the front has to be able to pivot up and down. There are several guns designed in this fashion, S&W autos a primary example. This keeps the factory from having to use an oval bushing at the front, and they can quickly ream it to size, dead round. It supposed to help with accuracy over this, too.

James K · July 11, 2013, 10:47 PM

I first thought the depression was just to allow the barrel to tilt. But as I checked further, I concluded that the tilt could be accomplished with a much shallower depression and a thicker barrel. The only reason for that deep a cut seems to be to allow dismantling.

Of course, in any pistol with a tilting barrel (Browning type), the front of the slide or the bushing has to allow for that tilt, which means that the lower front of the slide hole or bushing has to be cut out. (That is an important part to remember when fitting a bushing on an M1911 type pistol.)

Interestingly enough, the reason for the bushing on the 1911 is not for accuracy but because a big hole is needed to machine the locking lug cuts on the inside of the slide and the bushing fills up the gap. And some pistols, like the BHP, have bushings for that reason, although they are not removable. Pistols like the Glock don't need a large hole because they don't have locking lug seats that have to be machined.

Barrels that have a knobbed end to act like a ball joint for accuracy have the ball at the end, where it fits into the bushing, not part way into the barrel like the little Ruger.

Jim

July 10, 2013, 12:02 PM	#1
ragwd Senior Member Join Date: May 20, 2006 Posts: 925	LCP barrel thickness Hello all, thanks for taking the time to read my thread and all replies are appreciated. I am not a smith or a engineer. I do have a nice set of calipers and I know how to read them and I am a bit curious. I love my LCP, I have at least 500 trouble free rounds down range with it. So the proof that the barrel works well is evident. I am just amazed at how thin a section of barrel is. Outside diameter is .378 at the narrowest point and the inside diameter is .352 and the difference is .026 that divided by 2 gives me a barrel wall thickness at the thinnest point is .013 , that is about the same thickness of a nice business card. Is there a reason that they made it so thin, besides cost, although it probably cost more to to machine that depression than to not and leave it the same diameter as rest of out side diameter. Obviously it will hold the pressure but why ??? Is it because the pressure is not a issue at that point in the barrel and they used the extra room created to reinforce the slide at that point ?? I am betting it is something obvious that a novice like me doesnt see. Those numbers are just eye opening. Sorry for the long winded thread I just felt it necessary to explain my question. Thank you.

July 11, 2013, 07:31 AM	#5
CowTowner Senior Member Join Date: October 17, 2007 Location: Cowtown of course! Posts: 1,747	The barrel on a Kel-Tec P3-AT is of the same design for the same reason James K mentioned. __________________ NRA Chief Range Safety Officer, Home Firearms Safety, Pistol and Rifle Instructor *“Today, we need a nation of Minutemen, citizens who are not only prepared to take arms, but citizens who regard the preservation of freedom as the basic purpose of their daily life......”* President John F. Kennedy

July 10, 2013, 12:49 PM	#2
James K Member In Memoriam Join Date: March 17, 1999 Posts: 24,383	Because the slide is so short, that depression is necessary to allow the barrel to be removed when disassembling the pistol. I have no doubt that the Ruger engineers made sure there is still enough metal for safety. Jim

July 10, 2013, 01:55 PM	#3
ragwd Senior Member Join Date: May 20, 2006 Posts: 925	James, thanks , and the fact that ive run so many down range proves that. but the fact that it is only .013 inches thick just says WOW to me.

July 10, 2013, 02:24 PM	#4
GJSchulze Senior Member Join Date: May 3, 2013 Location: Western New York Posts: 454	By the time the bullet passes the thin spot, the pressure has dropped a lot. Before it passes that spot, there is no (additional) pressure. But, wow, that is thin!

July 11, 2013, 01:58 PM	#6
GJSchulze Senior Member Join Date: May 3, 2013 Location: Western New York Posts: 454	And yet my XD 9mm subcompact barrel (3") has no such depression and looks to have thicker walls. I guess every design has tradeoffs.

July 11, 2013, 02:09 PM	#7
Dixie Gunsmithing Moderator Emeritus Join Date: April 27, 2013 Location: Ohio Posts: 1,923	Actually, the other reason for the 'knobbed end', as I've heard them called, serves the same purpose as a ball joint. When firing, with a cylindrically round front barrel busing or bearing surface, the barrel's rear end has to drop down to unlock, so in order for it to move this way, the front has to be able to pivot up and down. There are several guns designed in this fashion, S&W autos a primary example. This keeps the factory from having to use an oval bushing at the front, and they can quickly ream it to size, dead round. It supposed to help with accuracy over this, too.

July 11, 2013, 10:47 PM	#8
James K Member In Memoriam Join Date: March 17, 1999 Posts: 24,383	I first thought the depression was just to allow the barrel to tilt. But as I checked further, I concluded that the tilt could be accomplished with a much shallower depression and a thicker barrel. The only reason for that deep a cut seems to be to allow dismantling. Of course, in any pistol with a tilting barrel (Browning type), the front of the slide or the bushing has to allow for that tilt, which means that the lower front of the slide hole or bushing has to be cut out. (That is an important part to remember when fitting a bushing on an M1911 type pistol.) Interestingly enough, the reason for the bushing on the 1911 is not for accuracy but because a big hole is needed to machine the locking lug cuts on the inside of the slide and the bushing fills up the gap. And some pistols, like the BHP, have bushings for that reason, although they are not removable. Pistols like the Glock don't need a large hole because they don't have locking lug seats that have to be machined. Barrels that have a knobbed end to act like a ball joint for accuracy have the ball at the end, where it fits into the bushing, not part way into the barrel like the little Ruger. Jim