OAL and its effect on feeding

[benos]

A comment on the relationship between OAL and feeding in the reloading forums prompted this.

After I got a blaster and its mags all dialed in, I'd fine tune the OAL, with goal being to determine the OAL for the most reliable feeding.

The last step would be to fine tune the powder charge to make the Power Factor with the OAL I'd decided on.

I'd do the following steps for each pistol.

Pick (and number if you haven't already) your 4 best mags for testing.

With a 40 S&W, I'd load about 100 rounds each (so you have some extras for double checking close calls) for about 5 different OAL's: 1.170, 1.180, 1.190, 1.200, 1.210, for example.

To start, I'd load 10 rounds, all at 1.170, in each of the 4 mags. I wouldn't put in more than 10 rounds because as the mag gets fuller it becomes more difficult to discern subtle differences in feeding that are the result of the OAL.

Before shooting, pull back the slide and wipe the feed ramp with a rag so it's completely clean. Then shoot the 10 rounds out of mag #1. Open the slide and note the pattern made by the bullets hitting the feed ramp, paying special attention to the lowest hits. Make a table in your notebook, with the mags/#'s in rows down the left, and OAL's in columns across the top. in the corresponding square for mag #1 / 1.170, sketch the feedramp pattern caused by that OAL.

Wipe the feed ramp clean and repeat with 1.170 for mag #2, and record in your notebook. Now you see where we're going.

Repeat until you have shot all your mags with all the OAL's. At that point you will know which OAL will give the reliability for that pistol.

That's also a good way to test / fine tune your mags. Then end goal is for the bullets to hit the feed ramp dead center and as high up as possible.

be

[Corey]

whats your recommendation on powder loads during the OAL setup phase? just "enough to make it go bang"?

[ParaGunner]

Great info!

[Duane Thomas]

What sort of pattern should for be looking for on the feed ramp?

[Flexmoney]

whats your recommendation on powder loads during the OAL setup phase? just "enough to make it go bang"?

That's an interesting question.

I'd think you would want to use standard power factor (along with recoil spring) so that you would be comparing slide movement that was consistent with the final usage. In other words, you'd want full slide travel and spring compression?

[Jake Di Vita]

If you have a scanner and your old sheets available, I'd love to see how the information laid out on the paid would look. I'm kind of fuzzy on what pattern to be looking for as well.

[HI5-O]

In your tests, what was the outcome?

Where were the bullets striking the feed ramp as the OAL increased?

[Corey]

whats your recommendation on powder loads during the OAL setup phase? just "enough to make it go bang"?

That's an interesting question.

I'd think you would want to use standard power factor (along with recoil spring) so that you would be comparing slide movement that was consistent with the final usage. In other words, you'd want full slide travel and spring compression?

so you think just pick a load that could be close and try a few different OALs to see which feeds the best, then go back and fine tune the powder charge up or down?

This is what precision rifle shooters do to dial in a load for a rifle, so it would seem to make sense here as well...

[G-ManBart]

whats your recommendation on powder loads during the OAL setup phase? just "enough to make it go bang"?

That's an interesting question.

I'd think you would want to use standard power factor (along with recoil spring) so that you would be comparing slide movement that was consistent with the final usage. In other words, you'd want full slide travel and spring compression?

so you think just pick a load that could be close and try a few different OALs to see which feeds the best, then go back and fine tune the powder charge up or down?

This is what precision rifle shooters do to dial in a load for a rifle, so it would seem to make sense here as well...

Yeah. I guess it's possible that one load would be more reliable at a different OAL from a different load, but that would be pretty "out there". If the slide is cycling fully the bullet should hit the ramp at the same place (within reason) for each OAL. Bumping the charge up or down a little shouldn't alter that.

I noticed that my Bedell is pretty gunked up (hasn't been cleaned in a loooong time) and that usually leaves a nice patter on the ramp where the bullets keep it clean. If I break down the gun to clean it this weekend I'll take a pic so folks get an idea of the patter Brian is talking about. Howard Smith posted some pics like that a year or so ago and I was like "oh wow, what a great indicator that is!". R,

[benos]

whats your recommendation on powder loads during the OAL setup phase? just "enough to make it go bang"?

You want the pistol to be functioning like it would at or near the PF you will shoot at.

If you have a scanner and your old sheets available, I'd love to see how the information laid out on the paid would look. I'm kind of fuzzy on what pattern to be looking for as well.

Sorry, never saved any of details once I determined the best OAL for a particular pistol.

To see what it looks like, try 2 mags - your favorite, and a "back up" mag that maybe doesn't feed all that well. Check the feed ramp patterns for both and you'll definitely see differences between the two.

I'd also use the "pattern test" when tuning mags.

In your tests, what was the outcome?

Where were the bullets striking the feed ramp as the OAL increased?

Most of my SVI 40's fed the best around 1.180. As the OAL gets longer, the bullets hit the feed ramp "sooner," before the slide has had the time/distance to build up a little more momentum like it would with the slightly shorter rounds.

be

[fastarget]

If I am starting with a new gun and new mags, how do I go about deciding if it is the mag or the oal? Is there a sequence to follow?

[benos]

If I am starting with a new gun and new mags, how do I go about deciding if it is the mag or the oal?

I'm not following you there. Are you having feeding problems?

be

[Jake Di Vita]

If I am starting with a new gun and new mags, how do I go about deciding if it is the mag or the oal? Is there a sequence to follow?

The first thing I'd do is caliper the feed lip dimensions at the back and front and compare those against data of what they should be (info should be able to be found with a search).

[fastarget]

sorry be, I should have clarified.

New gun single stack 9mm, non ramped barrel. since my post and after reading the thread I started working step by step. The issue was not feeding the top round from slide lock. I have since decided to tune the mags first as much as my knowledge would allow, then cycled manually some rounds after using a black marker on the ramp surfaces. I need to do more, but it seems the gun prefers a shorter AOL since it is loading them all. I need to take it out as soon as the mud dries and all the snow melts. With previous rounds loaded to 1.16 the top round would always be the problem but the rest were fine in a 10 rnd mag. Time to refine.

I have loaded different aols to test. I was just unsure about what to check first with all being new.

Jack, thanks, I will look into those dimensions, I have polished the lips and feathered the front edge some so far.

Edited March 9, 2010 by fastarget

[Jake Di Vita]

Is the gun brand new? Might warrant some breaking in before you make any concrete decisions. Although mag maintenance is never a bad idea.

[fastarget]

Is the gun brand new? Might warrant some breaking in before you make any concrete decisions. Although mag maintenance is never a bad idea.

gun is new and tight, after giving it some thought, my approach is what you are recommending. I took those wilson etms and started working on them, it was the factor I could control the easiest. I noticed that when I checked the top round, there was a considerable scratch on it in one spot each time, front to back. The lips were sharp, so a bit of polish there has not hurt it, now you barely see the scratch when you cycle rounds. I need to get the dimensions correct next. Then get back to breaking in while checking the ramp contact.

[benos]

fastarget,

Single stack 9's are notorious for feeding problems in general. The problem is the rounds "fan" (more space between the bullets than the rims) in the mag. Which will be especially noticeable with a slide-lock feed. Because the slide doesn't have the momentum it has when the pistol is cycling.

That's why, I'm pretty sure, the Robbie (TGO) spent quite a bit of time designing a single stack 9 mag for Springfield Armory. You might do a little research on whether SA offers their one 9 single stack mag. If they do I'd definitely try them out.

On OAL and 9 SS feeding, a shorter OAL will usually help. (Let's the slide build a little more momentum before the bullet hits the feed ramp.)

be