BBTI cylinder gap tests coming.

[Shadan7]

Well, this past weekend we celebrated our first anniversary of the Ballistics By The Inch project, as noted on the BBTI blog. And we've made an announcement there which I thought would be of interest here:

Announcing the Cylinder Gap Test!

We’ve had a Single Action Army clone in .357 magnum modified to allow for adjusting the barrel position from a standard 0.006″ to 0.001″ to no gap (barrel snug against the cylinder). We have a dozen or so different ammunition loads in .38/.357, and we’ll be essentially repeating the BBTI procedure for each of these, with the normal gap then the minimum gap then without any gap, starting with an 18″ barrel and going down in increments of one inch to just 1″ . Actually, one slight difference – to make sure we get a better statistical sample, we’ll be firing 10 (ten) rounds of each type of ammunition at each point rather than just 3 (three) as we did with the BBTI tests. Because we are limiting this test to just one caliber, we thought this was a reasonable step to take. We hope that this will allow us to conclude with some actual data what the effect of having a cylinder gap in a revolver actually amounts to.

We’ll probably be conducting these tests in the spring of 2010, and if past experience is any guide will have the new data sets available on the BBTI site sometime a couple of months later.

If you're not familiar with our project, take a look. And there are some more musings about future tests we're interested in in that blog post.

Cheers to all - thanks for helping to make our project such a popular reference (we crossed 1.5 million hits about two weeks ago!)

Jim D.

 

[unspellable]

Already done this the easy way.

Already done this the easy way. Used a Dan Wesson 44 Mag & 22 LR, they come out of the box with an adjustable cylinder gap. Didn't have a 357 DW to hand at the time. Used a Browning 5 inch Buckmark as a reference point for the 6 inch DW 22.

Don't have the data to hand since I just moved and stuff is in storage, but as I recall the gap didn't make as much difference as you would think until it got ridiculous. At 0.012 inch the 44 Mag started spitting crap back in my face.

10 rounds does not a good sample make. You need 30 rounds from a single shot for a good sample. (At 30 rounds the sample standard deviation begins to approach the population standard deviation.) With a revolver you have six different chambers to consider. At minimum you need to keep track of which shot came from which chamber. I fired 5 rounds from each chamber at each gap and considered it a skimpy sample.

 

[Shadan7]

Well, unspellable, if you do find the data and want to make it public, I think that'd be great, particularly since it is for two calibers we aren't planning to test. In the meantime, I think we'll continue on with our plans, and put the data up on our site when it is available.

Cheers!

Jim D.

 

[unspellable]

data

I'm not adverse to publishing the data. The rub is that I left Iowa for Alabama on short notice and had to throw every thing into boxes. The wife and dogs are still in the house in Iowa and I rented an apartment here. The bedroom is serving as storage and it's stacked high. Your guess as to where that data is located is probably better than mine. But one of these days I'll get it organized.

(I'll have to get it at least semi-organized before the wife and dogs arrive for a visit.)