Author Topic: How I measure leade for a bullet and barrel. Example: RMR HMW 147 in shadow 2  (Read 1991 times)

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Offline nkresho

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Good Morning Everyone,

Thought id take a stab at contributing something useful to the forum here.  You all have put so much info on here that it's like a library.  I am happy to take any constructive criticism and adjust my method (or this writeup) accordingly. 

I've been hand loading for 15 or so years to some extent.  Mostly pistol, but some rifle now and again.  I do not claim to be highly knowledgeable in this area, although i have done it quite a few times and i'm pretty comfortable recommending things like this to others.

With the short leade in these CZs we all know and love, I need to get a good load matched up to my barrel.  That's made more difficult by my desire to load heavier bullets.  I really enjoy the way 147s feel when loaded to approximately 130PF.  I keep my rounds at about 870-900 fps for about 133pf.

Enter the rocky mountain (RMR) 147 grain match winner bullet.  It's a flat point I've loaded up previously for subsonic suppressd shooting.  I like the accuracy and the nice round holes it makes in paper.

Here's how i calculate the proper OAL to use based on this specific bullet type:

Step 1, initial check, check that your current loads pass the plunk test.  Remove the barrel and make sure it's clean and dry.  I like to use 91% isopropyl alcohol and bore brushes.  Scrub it down to make sure it's spotless.   Hold the barrel vertically, with the muzzle end down.  Drop the loaded case into the barrel (makes a plunk sound).  Flip the barrel (muzzle side up) and drop the round out.  If it drops out, you're halfway there.  If not, the bullet is very likley touching the rifling and is too long.  If it does drop out, i prefer to reinsert the round again, and see if i can spin it gently with my fingers.  This is redundant in most cases, but it's how i like to second-check my work.  To check for how it should feel you can also use a clean and resized case with no bullet to spin.  Put that empty brass case in the chamber and give it a spin.  No resistance is what you're going for here.



If your rounds are good, i recommend loading one longer, to build in a margin of safety.  As i've read around, go 0.015" longer than your expected OAL.  Repeat the plunk test above.  If that longer round drops freely and spins freely, your load is good to go and you can proceed in mass-producing it.

Please be mindful, here, that changing OAL will probably change your velocity.  New OAL will ned a new chrono test to make sure it's doing what you want it to do.

Step 2, if the plunk test fails or you're starting from scratch, i'd start here.  Load some dummy rounds at various lenths.  I'd recommend starting where you want to load.  For example the loading manual recommended load.  Check SAAMI specs here too, to ensure you're not over or too far under.  Too far under will cause feeding issues with some barrels in my experience.  Too far over and the rounds won't fit in the magazine.   be careful with any oddly molded bullets too, here's an example of a rounded one.  This rounded tip would give a higher OAL reading when measured, but the seating die doesn''t touch that area, so the bullet is actually a tiny bit deeper in the case.



First, size some brass, same headstamp if you can. Then flare the mouth if needed.  Use a single stage press or use your progressive one stage at a time do accomplish this.  Load some rounds with your bullet seater set way out longer than you'd intend to load.  I load at about 1.160 or longer.  Then set your seating die to just touch the bullet.  Crank the seating die adjustment an 8th or 16th rotation at a time and measure OAL each press.  Get the round to your desired length and lightly crimp as you would a loaded round.  recheck the OAL and label the round (i like the fine tip sharpie for this).  Then load another until you have a set.  I like to have a set in increments of 0.005 so i can test all my barrels (i have a few CZs)



After the rounds are loaded to the predetermined lengths, crimped, and labeled, I highly encourage checking in a gauge.  Hundo gauges are a tad loose for me, so i use a wilson or lyman.  Mine here is a lyman.  Make sure they fit the gauge and triple check OAL before using as your " chamber leade gauge".





Once you have a set made up, plunk shortest to longer until you get a failure.  At that point, back it off until you get one that drops and spins freely.  Subtract 0.015 from that OAL and proceed with chrono testing, accuracy testing, and ultimately mass-production.  You'll want to chrono your loads at this OAL and determine what powder load you are going to use before loading hundreds or thousands of them as well.

« Last Edit: January 27, 2023, 05:39:34 AM by Wobbly »

Offline Wobbly

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Welcome Aboard !

Good, clear write up.

That's a way you can certainly do it. Basically you are dropping varying known cartridge lengths into the chamber until they spin freely. This requires that you have and maintain a selection of test cartridges for each bullet that you shoot.

While this system obviously gives workable results, and is great for commonly used bullets... IMHO it's not right for me. What if you see a discounted box of 50 bullets at your LGS and simply want to try them? Are you going to use 10-15 to maintain test cartridges for a bullet you'll never buy again ? And making that series of test cartridges is a lot of work for a new reloader that hasn't gotten far enough down the road to have an idea of what their favorite bullet is going to be.

The system we outline on this forum uses 6-8 bullets to achieve a number/ a reading. When that number is found (for that bullet in that barrel), all the bullets go back into the box to be used. Nothing is maintained. At that point we subtract 0.015" from that Test Length to get our Max OAL. You are then free to use any OAL between 1.000" and the newly found Max OAL. That is the Science of Reloading. Then, based on your knowledge of your gun's feeding characteristics, the caliber, what the wife tells you, how you feel that day, etc. you are free to choose an OAL you feel will serve you well. That is the Art of Reloading.

Nothing wrong with either method, but ours delivers a definite, fixed number. This is important for me because the last time I loaded the 147gr Match Winner, I ended up with a 0.010" OAL "window" between Max and Min OAL. I was able to split the difference and get the job done. That was for my LEO nephew that had a 40cal Glock. He was changing departments and the new assignment used 9mm. So we bought a drop-in barrel for his Glock and I made the ammo recoil the same as the 9mm Federal he was going to be shooting when qualified. He made the transition successfully and easily qualified.

All the best !
In God we trust; On 'Starting Load' we rely.

Offline nkresho

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Thanks, yeah, i can see where it's a bit overdone in some aspects.  I tend to load a few thousand at a time and stick with one or two profiles per weight.  I recently replaced a TSO i was loading for with a new shadow 2, and having these preloaded cases was convenient to see if i was far off.  I usually order 2000 to 5000 bullets at a time and tend to stick with the same ones once i get a load i prefer.  I changed over from the PD 147 V2 to the RMR HMW due to price and availability and have stuck with them ever since.

Alternatively, using these pre-measured cases would be helpful when reaming a chamber throat too.  You could drop your reference round in and see if more reaming is necessary.  I've toyed with that idea too, but carbide reamers are not readily available without a huge wait time.

Offline Ron IL

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That's like making your own go-nogo gauges.  At one time I had three Swiss K31 rifles.  I started reloading for them. All three were different chambers.  So I loaded for the shortest one and worked in all of them.  I used the method of putting a bullet in the case with a loose fit and chamber it closing the bolt slowly and smooth.  Remove it and measure.  Then shorten it by .015 for your load.  Nothing like slamming a round in and not chambering right and pull the bolt back with the bullet stuck in the rifling and powder everywhere.  :)
Ron
KB9TF
Retired Southern IL coalminer

Offline nkresho

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Yes, I guess I could have clarified it was more manufacturing a set of gauges for a specific bullet profile.  I do measure the leade indirectly through this.

I have a handful of 9mm CZs that I shoot my hand loads through.  My shortest is the p07, with the longest being by sp01 tactical.  For me, I am more likely to get another pistol than to change the bullet I use. 

Another part of the motivation for doing it this way is i've been looking lately at getting a carbide reamer so i can make them all the same (as long as my longest or slightly longer).  But, what i have been loading lately works fine, so the motivation to do this has been pretty low.  With the reamer, the pre-measured cases would be useful in determining how far to ream.

Additionally, FMJ 124s and even 147 FMJ are rarely an issue for OAL in my barrels, it's just these bigger flat nosed 147s.  With the RMR HMWs, some cases (CBC, red army, aguila, etc) can bulge when loaded too deeply, due to the internal taper.  I tend to get 1-2% bulge rate when loading to 1.080 or less with these cases.  Not every case with those headstamps, but more prevalent with those, specifically.