Minium distance bullet to lands/grooves

[GrinerBros]

Trying to make some more accurate loads for slow fire by extending the lenght of the bullet in the case. A buddy says 5 to 10 thousands is the minumum. Any opinions out there?

Information

Warning: This is a relatively older thread This discussion is older than 360 days. Some information contained in it may no longer be current.

[MEHavey]

He's right on. Start at 10/1,000 and move in 2-3/1,000 at a time to see if any significant difference.

I'd not recommend below approx ~3/1,000 unless you work up a load very deliberately engaging the lands. You'll be fighting manufacturing tolerances at that point.

Two asides: Are you using a Hornady/StoneyPoint (or equivalent) gauge to determine seating length for the rifle at these distances? And are you using a bullet ogive comparator (rather than just vanila OAL) to measure seating?
Hornady

[limazulu]

Some like .005 some like .020. You just have to make up difffernt loads of different lengths and try them. Just don't get them against the rifling as that can increase pressures.

[Bill H]

Your gun will determine the proper distance.

Sometimes, you can jam the bullet into the rifling and get good results. Other guns/loads like some separation. You just have to experiment to find the best distance.

If you have the bullet seated into the rifling, work up your load carefully, as this situation can cause higher pressure than when the bullet has some clearance.

What I would not recommend is having the bullet barely touching, or just a couple thousand off. In my experience, this is not accurate, and I believe it is because a small difference means some are touching, some are not, and this seems to produce fliers.

[GrinerBros]

He's right on. Start at 10/1,000 and move in 2-3/1,000 at a time to see if any significant difference.

I'd not recommend below approx ~3/1,000 unless you work up a load very deliberately engaging the lands. You'll be fighting manufacturing tolerances at that point.

Two asides: Are you using a Hornady/StoneyPoint (or equivalent) gauge to determine seating length for the rifle at these distances? And are you using a bullet ogive comparator (rather than just vanila OAL) to measure seating?
Hornady

Actually I'm using neither. I used a sized case without powder or primer and closed the bold to get a OAL to the lands/grootves. I will back off 20 thousands and start there.

Thanks to all who have contributed.

[MEHavey]

Please avoid using that method (seating a bullet in an empty case and closing the bolt to force the bullet against the lands and into the case). It will not (repeat, not) give you a reliable reading.

Two things can happen: (1) The bullet is actually engaged well into the rifling instead of right at the lands by the bolt closing--giving you a long reading; (2) the bullet is pulled slight out of the case by the groove engagement when the bolt opens -- giving you an even longer reading. In either case, you are not dealing with good data. And at the clearance distances you are dealing with, that can get real exciting.

Invest in the Hornady cartridge AOL tool (and matching case). You'll get accurate measurements that you may otherwise be betting your health on if wrong.






postscipt: I did the "smoked bullet" trick and/or the cleaning rod technique for years. That's when I was young and really [not very smart].

[slamfire1]

Over twenty years ago I was at the range, and a gentleman was shooting near on a bench. I noticed that he did not do a lot of shooting, rather he spend a lot of time waiting.

Being curious, when he was packing up I walked over.

This guy owned his own machine shop and was into super precision shooting. Everything in his rifle was trued, blued, match tattooed. (I forget the actual modifications). I do remember that he loaded his cartridges so that case head stamping were always in the same orientation in the chamber. He was also shooting exactly one minute between shots.

He was shooting five shot groups, the only difference in the groups was the seating depth. You could clearly see in his target sequence a reduction of group size, as depth increased. At some seating depth the targets began to grow again in size. In between those groups was the best target.

So here is the thing. I don’t believe that there is any hard and fast rule of seating depth that gives the smallest target. You have to find that yourself. And then it changes again. As your throat wears. I believe that the perfect seating distance can change depending on the new throat contour and seating depth.

[Matt Anthony]

For my bolt guns, using the RCBS Precision Mic, I start at .002 from the lands and seat back until the rifle groups. This method has always worked for me and only requires around 20 rounds to find that sweet spot.
What's funny is if you decide to change powders, primer brand and case manufacturer, your groups might not be the same, components do change group size, but that is not always true.
On a 222 Rem. 40X benchrest rifle with a Krieger barrel, Benchmark and H322 print the same size group seated the same distance from the lands. I am running the Benchmark cartridges 100 ft. per second faster than the H322. Point of impact is slightly lower with the H322 compared to the Benchmark.
Matt

.

[USSR]

You can deal with this two ways. You can establish your charge weight and then play with OAL (as probably most guys do), or you can establish your OAL and then play with your charge weight as I do. Assuming you are not restricted by magazine length, I like to be .010" to .015" off the leade and not any closer. Why? Because the ogive location varies among even the best match bullets (and Sierra MatchKings will vary by up to .010"). So, if you are trying to load just a few thousands off the leade, you stand a good chance of having some of your bullets touching or into the leade. Not particularly suited to accuracy.

Don

[MEHavey]

I agree w/ USSR above. You don't want to be so close that manufacturing tolerances come into play and you engage the lands unexpectedly. That's why at small stand-off distances (<0.003"-0.004" let's say), you want to have a bullet comparator to determine seating depth rather than using gross OAL.

I'll go home tonight and measure up some 168 SMKs (w/ the comparator) to check ogive/engagement variations in a batch/between batches and let you know. I'm kinda curious myself.