My Agency wants to reduce the size of our current M4 rifles from 14.5" to 10.5" rifles for entry purposes. We have access to order SMG UMP40 for close entry but management is dead set on getting 10.5" M4 rifles. Anyone have any advise on the 10.5"/11.5" M4 platforms? The ammo selection in limited only to 55gr. fmj nothing else. There is no other option to aquire different ammunition that best complements the shorter barrel and we can only aquire Colt weapons.

pancho, I cannot give you much direct info, since I have only used my one 11.5" AR.

But there are several threads here discussing the metrits of the 10.5, 11.5" 5.56 AR15/M4

Including:

This occasionally  interesting one

and

This one which has many embedded links and is a great reference


Just wish I were deciding between the UMP40 and the 10.5" M4

The first question is whether you actually need the shorter barrel.  If you find it to be a good fit for what you do, then we are on to the next consideration.

I have test fired a UMP in .45 caliber.  It has very excessive recoil and stock flex, and the weapon porpoised like you wouldn't believe.  When you consider the world's worst trigger, it was an all around flop.

I consider short barreled carbines to be supremely useful.  The 10.5 will have all of the terminal effectiveness that law enforcement requires.  Overall, it will do a lot more damage to a person than a pistol caliber will, regardless of the platform that delivers the bullet.

A word on ammunition selection.  Our ammunition forum is full of advice, but for the short barrels, the best advice is to get Hornady 75 grain TAP, in the NATO pressure.  Good stuff.

If you wish to go with a 10.5, or an 11.5 for that matter, you have lots of options, of which a few are good.  Colt makes 10, 10.5 and 11.5 inch barrels, available from Specialized Armament (SAW)in Chandler, and LMT sells 10.5s.  The best source for LMT uppers is Wes Grant at MSTN, available here on the Industry board.  If you go MSTN, you will need to aquire lowers from some one else or use what you have.

The downside to a short barrel is that the timing will often be off.  Although my own short barreled experiences have been trouble free, many people see the need to install a heavier buffer to delay unlocking and a stronger extractor spring to ensure reliable extraction.  SAW and MSTN both see to this in their builds.

Lastly, John Noveske makes an excellent 12.5 inch barrel that has roughly the same muzzle velocity as the M4 that you are using now, but is shorter, more accurate and retains accuracy longer.  Retail on these is 330 dollars.  They are not for the budget minded, but they are the best.  They are available from Wes at MSTN, assembled into uppers.

There are a lot of brands and other issues that I see fit to omit at three in the morning, but if you have any questions drop me a line through site IM.

I would take a look and contact MSTN and CMMG off the Industry or EE forums, as MSTN is producing SBRs for the security folk in Iraq (and already has many in use there) and CMMG is also doing the same. Both specialize in 1/7 twist, ramped SBRs.

They are two excellent dealers and very informed on SBRs and would I suspect be be very helpful to ya and your agency.

BTW, once the length drops below 14.5" it is no longer referred to as a M4, which has specific features that are lacking on the SBR AR15/M16 and are infact closer to the old XM177 specs, save the faster twist.

I would as I'm certain the dealers above would agree make sure you go with the 1/7 twist as it will allow the use of not only lighter weight rounds for cheap practice but also the heavy weight 77s and 75grn. rounds which are so popular now days.

Good luck,
Mike

Sounds like a no-brainer to me. If you already have M4s in stock, using 10.5 uppers will allow you to retain full muscle memory with the entry platform, it will allow swapping sights and accesories, you only have to buy one type of ammo, and maintainance will be much easier.

Are they talking about replacing the whole rifles or just the uppers?

If you're going with the whole rifle I'd look at the Colt 6933.

IIRC 55gr FMJ has 0 (not a typo) yards of fragmentation range out of a 10.5" bbl.  40 yards in a 11.5" bbl.  If you're stuck with 55gr FMJ, is it possible to persuade them to add an inch to their specified barrel?  I own a 11.5", and it's very handy.

Good luck.

Here is another one for you:
MY TAKE ON THE MK 18 MOD O, UPDATED VERSION WITH PICS  

The answers that you are looking for may not be in the Topic, but I am sure if you contact some of the individuals posting in the topic they may be able to help you out.

Good Luck,
"Capt Richardson"

Quoted: My Agency wants to reduce the size of our current M4 rifles from 14.5" to 10.5" rifles for entry purposes. We have access to order SMG UMP40 for close entry but management is dead set on getting 10.5" M4 rifles. Anyone have any advise on the 10.5"/11.5" M4 platforms? The ammo selection in limited only to 55gr. fmj nothing else. There is no other option to aquire different ammunition that best complements the shorter barrel and we can only aquire Colt weapons.

From what you're telling us, your choices have already been made. i.e. Colt ONLY / 55 grn FMJ ONLY.  I would stick with the 11.5" barrel instead of going with one of the 10" SP models.  It looks like you're going to end up with a short, fast handling carbine and pitifull ballistics.  I hope your job description warrants the trade off.

Quoted: From what you're telling us, your choices have already been made. i.e. Colt ONLY / 55 grn FMJ ONLY.  I would stick with the 11.5" barrel instead of going with one of the 10" SP models.  It looks like you're going to end up with a short, fast handling carbine and pitifull ballistics.  I hope your job description warrants the trade off.

Shit, i totally missed that. If you're confined to 55gr. FMJ, forget about short uppers, just take the 14.5 inside.

Why do the uppers have to be Colt? LMT makes the best 10.5" out there.

Contact LMT direct and see what kind of LE price they can give you.