Accurizing--How Much Help from Slide Rails?

I'm getting some frustrations in trying to accurize a 9mm with a linkless lockup. Barrel to slide seem solid but the 50-yard groups are still bad, pretty much unchanged. 5-8 inches with Hornady and Sierra bullets, usually FC brass.

With an aluminum frame I have some concerns about the traditional peening and centerpunching of the frame and slide rails. Mostly longevity but I AM unafraid of applying a few light taps every thousand rounds or so.

But I am wondering if anyone has tested through the process and noted how much each type of tightening up helps tighten up the groups. I really thought that if the barrel is wedged into the slide the same way for every shot, and the sights are on the slide, then it should matter not very much at all if the slide is loose on the frame.

Thoughts, experiences, MEASUREMENTS???

Thanks!

I'm of the opinion that a tight frame to slide ONLY matters in a Ransom Rest. If you properly fit barrel to slide and excellent snug bottom lug to slide stop fit the pistol should be capable of excellent groups from hand. I've shot in the 880's with loose frame to slide fit pistols. I build many pistols for people that aren't interested in getting the frame to slide tightened and they shoot excellent from hand. I fit the bottom lugs to force the vertical play out of the slide and in most cases it will limit some of the horizontal play. I've been doing a lot of PPC 9mm pistols lately and am regularly seeing that the bullets need a lot of velocity to shoot well. Getting 1" groups with what I consider warm loads and the groups are growing quickly with lighter loads. 9mm is a pain in the rear. 
Jon

Hello GrumpyOldMan,

Have you thought of using the Accu-rail system for your aluminum framed M1911? I have used it twice on lightweight Commanders with great success.  It tightens the slide to frame fit, bearing is steel to steel, it can be adjusted for wear (buy an extra set of rods) and is not costly.  I highly recommend them.

I aggree with Jon on what it typically takes, velocity wise, to make an accurate 9mm load in a M1911.  That's why I rather shoot an accurate and mild .45 ACP than an accurate and snappy 9mm.

Jim

Um, it's not a 1911.

Wanting to get info without it being tainted by mentioning brand name, I will remain silent on the make, but will repeat "9mm with a linkless lockup"

No barrel bushing, but like I said, the barrel wedges in there nicely when in battery with the slide.

I have tightened the horizontal slop at the barrel hood (only when locked) and have a temporary shim of surprising thickness to make sure the barrel is pushed all the way up. The cam locking surface starts moving the barrel backwards immediately when I press the barrel/slide assembly down into the frame.

I just might tighten it up a tiny bit more on what functions the same as the barrel legs/slide stop pin interface does on the 1911.

I posted elsewhere for accurizing tips brand-specific to this pistol a while back, on multiple forums, but the only suggestion was to buy a barrel.

What kind of gun is it?

I'm guessing, Glock/MP 9/ or Beretta?

This is like a poorly written mystery novel....

GrumpyOldMan states that it has an aluminum frame; so I would say no to the Glock or MP.  I would guess Beretta.  As an aside; I believe that the Accu-rail system has been used successfully on those.

It is sort of hard to help with only partial information.

My 3rd year at this but off last year due to injury and surgery.  Though I come from 45 years on the rifle. My ball gun is so snug on the link fit I have to wallop it on the but while holding the slide to open it. It will wear some and get easier to open. Tricked it out to the max. On the bags it groups one ragged hole at the 25 and holds the 10 ring at the long line. But stand up on my hind feet and shoot the thing is another story. So how does your Sig style pistol do bagged?

Hate to tell you this, but if a link is tight it's not properly fit. Barrel lugs are supposed to be tight, not the link. The link has two missions in life; pulling barrel down out of battery during recoil or when hand cycling slide and the link rides the slide stop pin as the barrel goes up into battery or lock up. The link is supposed to prevent bottom barrel lugs from battering on the slide stop pin. The link basically provides a smooth transition for the barrel in and out of battery. The link at no time is supposed to be tight. It is not supposed to provide lock up. Poorly fit barrels have in some cases intentionally had long links fit to make it lock up tighter, but this doesn't provide the same level of bottom barrel support as having both of the bottom barrel lugs provide lock up. Link lock up allows the barrel to twist during recoil. I have seen pistols with long links shoot fairly good if upper lugs and hood were fit good, but not my choice for a BE pistol. 
Jon

Jon Eulette wrote: 9mm is a pain in the rear. 
Jon

  I agree with Jon...
In 2001 the Richmond two man police team set a national record at the Jackson, Miss. Nationals, with a pair of 9mm long slides that held for 10 years..That was early in the 9mm surge in PPC/Bullseye popularity. Those guns were the closest frame and slide fit I could possibly manage, extremely close, yet very smooth cycling. Surface ground and scraped fit.   Those were the first two automatics ever,  to  win the two man team world cup at the nationals in Jackson..Both shooters, Jason Yarema, and Mike Talbert  had less than 5 years national level shooting experience combined between them, but, both were far above the average shooter.  
I didn't  like the 9mm then, I don't like it now, and stopped building/working on them long ago.
I am, though, an advocate of very close slide to frame fit. It's an old debate I feel originated with Kuhnhausen's statement that fit only accounts for 15% of the mechanical accuracy. I don't agree with him, but I also realize  he wrote that long before the machining/fitting techniques that we use today. There are many areas of his book(s) that don't apply today, as we have gotten better at the game..    For older, worn guns, squeezing and peening is so archaic, it's not worth mentioning..
Krieger Accu Rails are far superior, and will give the best frame to slide fit next to a machined/fitted frame and slide.
Jerry

Let me rephrase that. The link ops fine and free. The bottom lug fit is very snug.

It's a SIG which at 25 has always been a reliable 2-inch group shooter.

We all know that won't do at 50, especially when like many, this one doesn't have a strictly linear cone of dispersion.

So I'll get grumpy. It's linkLESS and the front bottom of the barrel camming surface lifts the barrel on contact with the disassembly lever when it's in the "closed" position, similar to how the barrel legs on a 1911 engage the slide stop pin.

Even though the barrel seems to be solidly held at the muzzle and at the ejection port when locked up, accuracy is not improved.

So if Mr. Kunhausen says 15% of the accuracy improvement in the 1911 can be obtained from the slide to frame fit, do I expect to reduce my 50-yard group sizes by 15% of the starting group size, or am I looking at 15% of the sought reduction from 5 inches to 2 inches?

15% of 5 = 3/4 of an inch tighter at 50.

15% of 3 = 0.45 of an inch tighter.

If I decide to take that plunge for what a this point appears to be a minimal improvement in accuracy, I am inclined to peen so the slide is driven UP into the rails rather than centered or bottomed.

Could the benefit be predicted by test-firing with an attempt to force the slide to the same position on the frame before every shot?

Some years ago, some of us noticed that barrel tester groups grew more than this mythical 15% when installed in the  finished gun. A barrel tester is very close to a rifle action as far as being solid and secure. The barrel does not/cannot move in a good barrel tester. The weak area, of the 1911, is, that the barrel is not fixed, secure and solid.. It moves, it shifts, and vibrates from lack of solid support.
The frame and slide are the foundation, support for the barrel. The more precise the foundation, the more secure the barrel. The barrel should not move, cam, or provide support for any part of the system. 
If the frame and slide permits  movement in any plane, other than the linear axis provided/allowed by the rails, the barrel will not seat and lock up consistently..and / or be a stressed condition.   30/40  years ago,   a 3 inch 1911 was considered great.. Today the groups are approaching 1 inch from good guns. Actually, not a great deal has changed fundamentally, except far better, more accurate machining processes.
Jerry

Look at my sig name.

Read the posts.

Would you guys PLEASE STOP POSTING METHODS FOR ACCURIZING 1911s?!?!?!?!?!?

Does anyone know what the weak area is in a SIG, with the Petter style lockup?

Now someone will post details on how to accurize a Beretta, just to piss me off and drift the thread. But if done right it might make me laugh. Maybe.

The best way to accurize a Beretta is to hold it upside down and pull the trigger with your pinky.

GrumpyOldMan wrote:Would you guys PLEASE STOP POSTING METHODS FOR ACCURIZING 1911s?!?!?!?!?!?

Does anyone know what the weak area is in a SIG, with the Petter style lockup?

Now someone will post details on how to accurize a Beretta, just to piss me off and drift the thread. But if done right it might make me laugh. Maybe.

Sorry, but from an engineering stand point the principle is the same. Some models/brands lend themselves to the necessary modifications better than others.
Goodluck with the SIG..
Jerry

Grumpy, did you try some of that fancy Atlanta Arms ammo that the AMU guys use for their Berettas for the Sig at the long line?

GrumpyOldMan wrote:Look at my sig name.

Read the posts.

Would you guys PLEASE STOP POSTING METHODS FOR ACCURIZING 1911s?!?!?!?!?!?

Does anyone know what the weak area is in a SIG, with the Petter style lockup?

Now someone will post details on how to accurize a Beretta, just to piss me off and drift the thread. But if done right it might make me laugh. Maybe.

You ask for help but get "grumpy" when people offer thoughts on different guns although you would not furnish a brand or model. Most problems get solved by posting all available info and drawing from peoples knowledge about that problem not playing a guessing game.

Weak area's of SIG barrel lock up: Upper barrel lug lock up is the ejection port (forward). The top of the barrel has a small flat bearing surface that allows rotating of barrel during firing (recoil)[Upper lugs on 1911 barrel are fit to prevent rotation typically with 2 bearing points to pinch fit slide and barrel]. Sides of hood would need minimal clearance (I'd shoot for 0.001" each side) for resisting barrel rotaion during firing. Hood (rear) to upper lug (forward ejection port)should be minimal (0.001-0.002"). Bottom barrel lugs would need to be a tight fit (wedged) to force play out of the barrel lock up pin (slide stop in 1911, not sure what SIG calls it) and the vertical play in the slide to frame fit.

If you could get barrel to fit like this I wouldn't be concerned about slide to frame fit. Also the barrel bottom lugs would need to keep the barrel in battery for around 0.100" of initial slide travel. I'm not sure if match quality oversized barrels are available, but you could TIG the existing barrel and refit it.

Ultimately if you had an oversized new barrel you could probably achieve all these fitting points. I've done trigger work on SIG Master Series match pistols and they are similar to what I've described and they shoot very well. In my opinion though I believe the 1911 to be a superior design for getting NM accuracy.
Jon

Rob Kovach wrote:The best way to accurize a Beretta is to hold it upside down and pull the trigger with your pinky.

Well done. Just what I needed.

DavidR:

I didn't get grumpy until after the post Tue Sep 02, 2014 8:52 am

Jerry then responded that the general principles are the same. Well, that's why I looked first to the lockup between the front of the barrel and the built-in notreallyabushing portion of the slide. I also looked at the barrel hood and took out some slack there.

Further examination of the bottom camming surface showed that it is already resting firmly on the disassembly lever. But in thinking about what we have learned about 1911s, I have now done a modification to try to reduce rotational play by relieving that surface in the middle. Intent is to make the wider cam-lock surface act like two legs and eliminate any high spot that could allow barrel rotation (despite two points of contact on the sides of the barrel hood, from the top of the slide).

And no, I haven't yet tried the Atlanta Arms ammo. I want only a box or two for control testing right now, but it looks like no one west of the Big Muddy carries it on the shelf. Other priorities prevent ordering enough to make mail delivery come in at a decent price.

Also closed up the horizontal play at the rear of the slide. Vertical will be another day. The front of the slide to frame fit looks like it's going to be a booger, in both planes.

Update:

Relieving the center portion of the barrel locking cam/takedown lever interface did not help much, but vertical dispersion for 4 out of 5 shots was better. Flyers in every group though, so I'm suspecting something else may be at play.

Looked a bit closer and decided that making a zero-clearance fit a the top sides of the barrel lug still allows barrel rotation on the takedown lever during recoil. Since the design takes that locking surface away from the lever immediately upon the beginning of slide/barrel movement, I looked at the chamber area of the barrel and the slide. Close up the gap there with a reversible shim method on both side and my one and only group single-loaded (Left the magazine home!!!) using XTPs still had a flyer making the whole group at 50 5.85 inches, but four of them were in a diagonal line only 2.4 inches center to center. One shot did go off early, but the flyer landed twice as far away as I called it.

There is hope. I tried to calibrate my expectations by looking up results for SIG X-5s and X-6s, but there are conflicting reports as to whether their 2-inch *or better* groups are at 25 or 50 meters.