advantages/disadvantages of roller delayed blowback system?


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Shootist16
January 18, 2010, 10:14 AM
Anyone care to comment? Seems that even HK is moving away from this design. What are the advantages and disadvantages?

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goldie
January 18, 2010, 11:37 AM
i have an hk91 with this system, the only thing i dont like is that the action is black after firing a lot. the bolt,carrier, & chamber really get dirty. the action is so strong that i dont think this grime can stop it from running.ive always noticed how much more it takes to clean this gun as opposed to an fal or piston driven gun.i remember reading once in a gun mag how someone said that because of the violent nature of the action, it would make for a short service life.but these guns are still going,so i dont think thats true.its also hard to say if theres more recoil or less, hk always advertised as this action having reduced recoil.they might be moving away from this action because it might be expensive to produce.roller locking bearings,many parts...

Z-Michigan
January 18, 2010, 11:44 AM
I had a PTR-91, and have used various gas operated systems.

Roller-delayed blowback BENEFITS:
-generally reliable when used with ammo that it "likes"
-no moving parts up front, so barrel can be free-floated
-no hole to drill in the barrel for a gas port
-relatively cheap to manufacture (though you wouldn't know that from HK prices)

DRAWBACKS:
-generally ammo sensitive, both to bullet weight and to case type. Switching ammo can cause reliability problems.
-extremely dirty in operation, at least as bad as an AR-15 if not worse
-requires a relatively heavy and complex bolt carrier; overall system is not any simpler than a simple piston system like an AK-47
-hard on brass, due both to chamber flutes and violent ejection
-very high cocking effort when bolt is fully "locked" forward (rollers fully outward)
-lack of a gas port doesn't necessarily benefit velocity due to speed of unlocking (unlocking starts while under high pressure)
-locking strength varies as parts wear (arguably also true to some extent in piston/locked bolt systems, though for different reasons)
-no benefit in perceived recoil compared to a well designed piston system
-recoil felt can vary depending on how clean/dirty chamber is and precise details of the cartridge case
-using significantly different bullet specs (weight or velocity) requires tuning and changing out the locking piece and/or rollers
-not user-tuneable like a piston system with an adjustable gas regulator is

ChronoCube
January 18, 2010, 11:44 AM
One advantage is that it will be inherently more accurate compared to a gas operated rifle because there is no gas tube hanging off the barrel, affecting barrel harmonics.

Z-Michigan
January 18, 2010, 11:49 AM
One advantage is that it will be inherently more accurate compared to a gas operated rifle because there is no gas tube hanging off the barrel, affecting barrel harmonics.

Although I can see this in theory, I note that there are lots and lots of AR-pattern guns shooting sub-MOA, some around 1/2 MOA, while I cannot name any roller delayed guns regularly shooting better than 1 MOA. The flexible gas tube on the AR pattern doesn't seem to affect the barrel's free float to any meaningful degree.

Shung
January 18, 2010, 11:58 AM
I cannot name any roller delayed guns regularly shooting better than 1 MOA

Stg57 + gp11 ? will do sub MOA I think. Wouldnt be mistaking, but it seems to me, if I translate correctly, that the SiG is a roller delayed blowback system..

but maybe it's just my english

Retro
January 18, 2010, 12:04 PM
Before expiring, one must own one of each:
1. PTR91 MSG90 roller delayed blowback system
2. LRT-SASS gas blow back system
3. M1A piston-operated system

:)

M1A is a bad word in my vocabulary now because my Supermatch is now shooting 3 MOA with match grade ammo after I shimmed the gas tube. PTR91 shoots consistently 1 - 1.5 MOA with match grade ammo (but make sure that sling does not hook on to that ridiculous ring attached to the barrel though, totally screws the harmonics). SASS shoots more or less the same as PTR91 but with magazine feeding issues (I am waiting for the new Magpul mag to arrive).

R

RedLion
January 18, 2010, 12:11 PM
Although I can see this in theory, I note that there are lots and lots of AR-pattern guns shooting sub-MOA, some around 1/2 MOA, while I cannot name any roller delayed guns regularly shooting better than 1 MOA. The flexible gas tube on the AR pattern doesn't seem to affect the barrel's free float to any meaningful degree.

The PSG-1 has to be able to hold better than 1 MOA to 300 yards, but for the price and scarcity it doesn't really count....

Shootist16
January 18, 2010, 12:56 PM
How about longevity? Does the roller delayed blowback have more or less wear?

Retro
January 18, 2010, 12:58 PM
there is minimal wear on the bolt itself, all the wear and tear are on the rollers, and once you replace the rollers, the headspace is back within specs.

Z-Michigan
January 18, 2010, 01:40 PM
Uhmmm, there is also wear on the trunion, which is not easily replaceable. They do however make oversized rollers that will make everything work OK for quite a while (longer than most people reading THR would try to keep shooting a .308). This is another area where I'm not sure a comparison is that important because the gas-piston rifles also last a very, very long time in their bolt mechanisms. For instance, the FAL has a projected receiver life of 80,000 rounds (the locking area is machined into an FAL receiver, so is not readily replaceable). I don't often hear of ARs wearing out their barrel extensions, but if they do it's a $10 part and 1-2 hours of work to replace it.

rcmodel
January 18, 2010, 01:45 PM
I never cared for them much for three reasons.

1. The fluted chamber makes a mess of brass for reloading.
2. The violent ejection makes finding the brass chancy at best anyway.
3. They are really loud, do too the high chamber pressure at extraction blasting out of the ejection port so close to your ears.

rc

stubbicatt
January 18, 2010, 01:53 PM
z-michigan stated for the record: For instance, the FAL has a projected receiver life of 80,000 rounds (the locking area is machined into an FAL receiver, so is not readily replaceable).

The FAL locking shoulder is a little button sort of arrangement pressed into the receiver. If it wears out, another can be replaced in less than 5 minutes.

The engineering in the Vorgrimmler actioned rifles is fascinating to me. I can't say that they are any better than any other sort of locking system. The recoil is the same as any other 308, IME. It is exceptionally easy to clean *if* one has the requisite equipment, especially the various brushes. Just wipe off the bolt and carrier assemblies, wipe out the receiver, re-oil with Ballistol, clean trunnion and breechface area, the chamber, and swab out the barrel. Voila. Easy peasy lemon squeezy.

The sights are a marvel, and have been "appropriated" in spirit by the new Nikonov rifle in Russian Federation. For what it is, a "people gun," it is really a super design. Exceptionally reliable, more than accurate enough, durable, and a pleasure to shoot.

Some complain of "ergonomics" and it does have its shortcomings, like most every "one size fits all" sort of military rifle. These can be remedied by some of the customizeable pieces readily available... the paddle mag release, the adjustable stocks, and the ambi safety seem to remedy any shortcoming I can think of.

YMMV

rfurtkamp
January 18, 2010, 01:54 PM
If you're into exotics, the roller-locked guns can be cut-down/modified to lengths in calibers that piston guns would cry over - the FAL, as much as I love it, just won't run on a 8.5" barrel, let alone the 51k guns that have been made.

In pistol-caliber carbines, the recoil is *substantially* less than comparable systems. Take a 9mm AR and a MP5. Guess which one is much more pleasant to shoot.

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