May 28th, 2019

AR Feed Failure — What Is Your Diagnosis?

AR AR15 mag magazine magpul jam misfeed short-stroking jam cartridge

Posting on the 6.5 Creedmoor Group Facebook Page, Russel T. complained that his AR magazine doesn’t like to feed that last few rounds. Russell asked: “Full magazine, no problem cycling. But with five (5) or less in the magazine… this happens. What can cause this?”

It sure looks like he could use a new magazine spring, but there may be buffer-related problems as well. Or maybe a gas system issue. What’s your call? Here are some responses posted by Facebook folks:

“Weak mag spring.” — Josh N.

“Weak mag spring or too heavy of a buffer spring.” — Justin G.

“Try a different mag, if it still jams it’s probably a gas problem, if not chuck the bad mag.” — Otto G.

“Weak mag spring or literally anything that would cause the Bolt Carrier Group to short cycle.” — Reggie W.

“I’ve had the same issue with my 300 BLK when my buffer tube came apart. It would still cycle cheap rounds fine but [not] the Hornadys. Took it apart and found the buffer tube was in pieces.” — Hunter R.

“Could be a weak mag spring or buffer spring, both at the same time.” — John S.

“As mentioned it could be a list of things. However, bolt velocity is too fast/hard and the usual (but not always) culprit is over-gassing.” — Bill F.

“Short cycle — clean and LUBRICATE the weapon.” — Mark H.

“Look to see where the brass is ejecting. That will tell if it’s an over or under gas issue. If that’s ok then look at the mag spring. See Diagram” — Teddy G.

AR AR15 mag magazine magpul jam misfeed short-stroking jam cartridge

“Weak magazine spring, I tossed four brand new ‘bargain mags’ [due to] that very problem.” — John V.E.

“May not be a weak spring or bad mag. Check out a Tubb Precision flatware spring. I swapped mine in a new rifle and solved the problem of short stroking and double feeds.” — Anthony T.

“It might be the follower as well, some designs will dip in the front/rear as rounds are expended. It’s the reason why we didn’t use some service mags with the green followers.” — Chris J.

“Weak spring… time for a new magazine…or add a 5-round block and make it a 25-round magazine. But I’m positive it’s a weak spring, which means it’s just a matter of time for failure.” — Steve M.

“Without the weapon in hand I would hate to guess….
Start with the simple stuff and go from there. Trying to diagnose a problem from a photo is just like when your wife or girlfriend tells you the car won’t start. LOL.” — Mark T.

Permalink Bullets, Brass, Ammo, Gunsmithing, Tactical, Tech Tip 4 Comments »
May 28th, 2019

Will Carbon Build-Up Inside Cases Raise Load Pressure?

Carbon fouling case cartridge interior Pressure volume ultrasonic

As a cartridge case is reloaded multiple times, burnt powder residue and carbon builds up on the inside of the case. Unless the case interior is cleaned in some fashion, eventually you’ll see a slight reduction in case capacity. One of our Forum members from Australia wonders about the effects of reduced case capacity: “If the capacity of the case decreases as the crud builds up, then it effectively reduces the size of the cartridge (inside). Wouldn’t that change the pressure produced from that of an equivalent clean case?”

Interesting Test of Case Capacity Changes
Forum member Fred Bohl has actual test results that can help answer the above question. Fred proved that, over a 20-reload cycle, the case capacity of uncleaned cases did decline a small amount. However, surprisingly, this did not seem to affect the actual chronographed velocity of the load. Extreme Spread (ES) did increase, but Fred believes the higher ES was due to changes in case-neck tension, rather than due to the slight reduction in case capacity. Fred reports:

“Back when beginning to use ultrasonic case cleaning, part of the motivation was to get the inside clean based on the assumption that allowing burnt residue to build up inside cases would affect capacity, and, ultimately, performance. An experiment was done to test this hypothesis. The load used, 30.5 grains of RL15 behind 107gr SMKs in a 6mmBR, was selected for best group and lowest ES in prior load development. It turned out to be 92% of initial case capacity and neither “full” or compressed. (I would suspect that different powders, load weight, and total case capacity might produce very different results.)

We took 30 cases of identical initial capacity and tracked three lots of 10 each:

LOT 1: No Internal cleaning
LOT 2: Cleaned with media in tumbler
LOT 3: Cleaned with Ultrasound machine

Each case (in each lot) was shot and reloaded 20 times. The simplified results after 20 reloads of each lot were as follows:

Lot 1 (not cleaned) – 0.3 to 0.4 gr. loss of capacity, 5 to 8 fps greater ES.
Lot 2 (tumble cleaned) – 0.1 to 0.3 gr. loss of capacity, 4 to 6 fps greater ES.
Lot 3 (ultrasonic cleaned) – no loss of capacity, no detectable change in ES.

FINDINGS
There was no detectable correlation of velocity change to the lots. An oddity was that on very hot days Lot 1 velocities were, occasionally, slightly higher. From results of another ongoing test, I believe the above differences in ES are probably due more to variance in bullet grip tension than case capacity. The ultrasound cleaned cases (LOT 3) did maintain the lowest ES, but we are not 100% sure of the reasons why. More consistent bullet seating might be the reason.”

Carbon fouling case cartridge interior Pressure volume ultrasonic

Editor’s NOTE: Fred’s results do suggest that carbon build-up inside the uncleaned cases might cause a slight increase in pressure that shows up on hot days. Fred has posted that: “A local shooter reported doing the 20 reload, no-clean test on a .308 that gave a loss of capacity of 2.0 grains, doubled ES and significant velocity changes. However, I don’t have any details on his load weight or powder.” Obviously a lot of carbon can build up with 20 reloads. Many shooters retire their brass before then.

Ultrasonic Cleaning and Neck Lube
Some time ago, Jason Baney did a lengthy test on ultrasonic cleaning. Jason found that with his ultrasonically-cleaned cases, the inside of the necks got so “squeaky clean” that he needed to use dry lube in the necks. Jason uses the $10.95 dry lube kit from Neconos.com. This applies ultra-fine Moly powder to the neck using small carbon steel balls.

Neconos.com moly neck lube

Permalink Bullets, Brass, Ammo, Reloading, Tech Tip 2 Comments »
May 28th, 2019

Not Too Late to Save — Memorial Day Sales Are Still Running

memorial day 10% off sale discount code brownells saving

Did you overlook your Memorial Day weekend shopping? There were some great bargains to be had at many of the USA’s best online vendors. But don’t fret. Many sales are still running, so you can take advantage of great sale prices. Here are SIX SALES that run through May 28th at 11:59 pm (or even later). But don’t hesitate too long.

1. Brownells — 10% Off $99+ and FREE Shipping

memorial day 10% off sale discount code brownells saving

Brownells is effectively extending its Memorial Day Sale by 24 hours. Through 11:59 PM CDT on May 28th, you can get 10% Off Orders $99+ with Free Shipping. this applies to ALL products — Use Code PTD.

2. SWFA — 10% Off EVERYTHING — Optics, Rifles, Ammo & More

SWFA 10% off sale guns ammo scopes Vortex, Schmidt & Bender, Kahles, Swarovksi, Zeiss, U.S. Optics, Leupold, Leica, Nikon, Burris, IOR Valdada

SWFA carries most of the top optics brands including Vortex, Schmidt & Bender, Kahles, Swarovski, Zeiss, U.S. Optics, Leupold, Leica, Nikon, Burris, IOR Valdada and more. SWFA also has a wide selection of rifles and pistols Everything in the store is 10% off through 11:59 PM CST 5/28/19. Plus FREE Shipping for $99.99+ purchases with code SHIP99.

3. Palmetto State Armory — 10% Off Guns and Ammo

Save on AR components, accessories, and ammo with Palmetto State Armory’s Memorial Day Sale running through 11:59 pm on May 28th (Tuesday). Get a stripped lower for just $39.99, or a complete lower with MagPul stock for just $149.99. There are dozens of other great deals.

4. Precision Reloading — $10 Off $100 or $30 Off $300

Through the end of the day today 5/28/19, at PrecisionReloading.com you can save $10 with Promo Code MD191 (for $100+ purchase) or $30 with Promo Code MD193 (for $300+ purchase).

5. Creedmoor Sports — Free S/H + 10% Off Creedmoor Items

The Memorial Day Sale at Creedmoor Sports is still underway. You get Free Ground Shipping and 10% Off Creedmoor-brand items. In addition, many other items are on sale.

6. Cabela’s — $10% Off Tuesday for Entire Order

This is a regular Cabela’s Promotion. Club members get 10% OFF the entire order with Code 19CLUB528. NOTE: You must be a Club Member.

Permalink Bullets, Brass, Ammo, Hot Deals, News, Optics No Comments »