Winchester MP4 CO2 rifle: Part 3

by Tom Gaylord, The Godfather of Airguns™
Writing as B.B. Pelletier

Part 1
Part 2

Today’s report is a continuation of the guest blog from HiveSeeker. Today, he tells us about the rifle’s performance.

If you’d like to write a guest post for this blog, please email me.

Over to you, HiveSeeker.

Winchester MP4 CO2 rifle

Daisy’s Winchester MP4 is a realistic and fun-to-shoot military replica pellet rifle.

This is the third installment in my evaluation of the Winchester MP4 CO2 rifle. The short version of Parts 1 and Part 2 is that this gun might be of interest to someone looking for a realistic AR15-style semiauto pellet rifle — as long as they can accept 1-inch, 10-yard groups and an intermittent ammo feed problem. I was determined to find out what was causing the ammo feed issue in order to minimize or eliminate it and was also certain the gun could shoot tighter groups with more testing. In Part 3 and also in Part 4, I make progress on both fronts.

This report covers:

• Catch-up
• The ammo feed problem
• Testing the ammunition magazine
• It’s the CO2 clip!
• Eliminating minor misfires

Catch-up
Before we continue, I want to add a couple comments that should have been included previously. First, in addition to the authentic realism of this replica gun, at 5.8 lbs., it hefts like a firearm. Most of the other military-style pellet rifles out there are lighter, and a number of reviewers mention that the realistic weight of the Winchester MP4 adds to its appeal. I agree.

Second (and B.B. was kind enough not to chide me for this), I failed to mention that despite the manual’s statement that no additional lubrication is needed for this gun once it leaves the factory, go ahead and put a drop of Crosman Pellgunoil on the tip of each CO2 cylinder when you install it. That will help keep all those seals healthy and happy for years to come.

The ammo feed problem
I hadn’t experienced the MP4’s ammo feed problems to nearly the extent of some other shooters, but I was determined to figure out the possible causes and eliminate or minimize them. I suspected that the problem might be related to either the ammunition magazine (which has an 8-shot rotary cylinder on each end where the pellets or BBs are loaded), or the CO2 clip (which holds the two CO2 cartridges). I already had a number of spare magazines and ordered six additional CO2 clips directly from Daisy Customer Service for testing.

winchester MP4 CO2 rifle mag and CO2 clip
Two ammunition magazines on the left. They have 8-shot rotary cylinders on each end that hold the pellets or BBs. On the right are two CO2 clips that hold the CO2 cartridges. The ammo mag slides into it. Keep all these terms straight for the discussion below! That little plastic CO2 piercing key fits neatly into the slot at the bottom of the CO2 clip cover.

Testing the ammunition magazine
While I initially suspected the ammunition magazines were the source of inaccuracy, one curious fact is that these are the same ones used by the Winchester M14 and they apparently work flawlessly in that gun. It got 14 out of 15 five-star reviews at Pyramyd Air. We’ll come back to the ammunition magazine in a moment, but suffice to say that I ended up testing 9 different ammo mags in each of 7 different CO2 clips and found no difference in their performance. None of the ammo mags were malfunctioning.

Winchester MP4 CO2 rifle testing
Ammunition magazines and some CO2 clips ready for testing in the Winchester MP4. A few pellets, too — that’s coming in Part 4.

It’s the CO2 clip!
The CO2 clips proved to be another story. When they arrived from Daisy, they were all in excellent condition, but it was clear that two of them had been used. When I inquired, I was told that not enough new CO2 clips were available, so two units were pulled from returned MP4s. This is not encouraging, but they were much cheaper than expected, so I had no complaints. I marked all 7 of my CO2 clips and got ready to test the new arrivals. Clip 1 is the already-tested original that came with my rifle.

The first shot using clip 2 (the first of the 2 used clips) was a major flyer, zinging well off my point of aim. Not an auspicious start. Second shot, no pellet — just air (which I’ve been calling a misfire and one of the few ammo feed issues I’ve actually experienced up to this point). The third shot was my very first jam with this gun. The ammunition magazine would not eject from the CO2 clip, and I had to eject the CO2 clip itself to get the ammo mag loose.

I was especially careful to reseat the CO2 clip solidly for my next try. Fourth shot was another flyer but not quite as bad as the first. Fifth shot was another jam. This one was worse than the first, with the trigger jammed solid and the ammo mag again not ejecting. This time when I ejected the CO2 clip, the ammo mag actually stayed lodged inside the receiver!

It was suddenly clear what had happened — a pellet was jammed halfway between the ammo mag’s rotary cylinder and the barrel, locking the ammo mag in place. Fortunately, I had a plastic rod for clearing jams. Sure enough, I could feel the pellet slide back a little and then the ammo mag simply fell out of the gun.

When I examined the magazine, both the noses and skirts of several of the pellets showed visible deformation. This was the first time I’d really experienced the frustration of other MP4 buyers who had ended up returning their guns. I’d had enough — I was done testing clip 2! (Note that Daisy Customer Service replaced this clip with a brand new one at no charge.)

Winchester MP4 CO2 rifle jammed ammo mag
The ammo mag was jammed in the gun, separate from the CO2 clip!

Winchester MP4 CO2 rifle damaged pellets
This is what a bad CO2 clip does. This jam was so bad that the ammunition magazine remained lodged inside the receiver even after the CO2 clip was ejected. Note the damage to the two pellet skirts, especially the one on the right.

With no small amount of trepidation, I shot a full magazine using original clip 1, just to make sure my gun had not been damaged. Thankfully, everything was back to normal.

I was ready to test CO2 clip 3 — the other used one. Except for being a little tight in the receiver (something I’d also noted with my original clip), it performed flawlessly with all 9 ammunition magazines. I did have to push harder for the ammo mags to click into place, but that was all — and this actually smoothed out by the time I was finished testing. My experience was identical with the remaining brand-new CO2 clips 4 through 7. They varied in how tightly they fit into the receiver and how tightly ammunition magazines fit inside them, but they smoothed out with just a little use. And after hundreds of pellets, I had only a few misfires, which I subsequently decided were my own fault.

Here’s my important finding: The worst ammo feed problems are probably being caused by bad CO2 clips. Either the CO2 clip itself is not seating correctly within the receiver, or ammunition magazines are not seating correctly inside the CO2 clip. Either will cause the pellet not to line up with the barrel, resulting in a jam or misfire. This also explains why the identical ammunition magazine performs flawlessly in the Winchester M14 (where it locks directly into the receiver) but suddenly starts having problems in the MP4.

The obvious conclusion is that a replacement CO2 clip just might fix a misfiring MP4. If you order one directly from Daisy, try to make sure you’re getting a brand-new one, as these performed flawlessly — though I only had trouble with one of the two used clips. Note: To add to the nomenclature confusion, if you order this part from Daisy Customer Service, both they and the exploded parts diagram refer to the CO2 clip as the “Puncture Unit” (Part 79).

Winchester MP4 CO2 rifle parts diagram
The Winchester MP4 exploded parts diagram. If you are ordering a replacement CO2 clip, it’s referred to as the “Puncture Unit” (Part 79).

We’ll take a minor detour as long as we have the MP4 parts diagram up. A number of reviews and blog comments describe the MP4 as a dressed-up Winchester M14. I initially thought otherwise, but the schematics prove me wrong. The barrel assembly and many other internal components appear identical. The CO2 clips share many parts as well. However, in the M14, the ammunition magazine slides freely through a hole in the CO2 clip and locks directly into the receiver. In the MP4, the ammo mag latches to the CO2 clip, which then latches into the receiver. As we’ve seen, having a middleman (the CO2 clip) between the ammo mag and the receiver is a potential problem. Besides the CO2 clip, the biggest differences between the M14 and the MP4 lie in the trigger mechanisms, receivers, and stocks and forearms.

Winchester MP4 CO2 rifle M14 parts diagram
T
he Winchester M14 does, indeed, share many parts with the MP4.

 

Winchester MP4 CO2 rifle M14 CO2 clip
These are Winchester M14 CO2 Clips. The ammunition magazine slides freely through a hole in the CO2 clip (circled) but does not click into it. Instead, the ammo mag locks directly into the receiver — no middleman here! An ammo mag is shown inserted into the hole in the clip on right. This CO2 clip can be misaligned with the M14’s receiver without affecting ammo mag alignment at all.

Back to the MP4. One Pyramyd Air review suggests that the ammo mag misalignment may be caused by CO2 pressure pushing the CO2 clip slightly out of position. This is certainly plausible and might also explain why this problem can worsen over time (as other reviews report) if increasing wear is occurring. If wear is occurring on the CO2 clip, a replacement CO2 clip could fix the problem. If wear is occurring inside the receiver — or should something actually be wrong with the receiver to begin with — then it’s time to contact the manufacturer or start picking out a new rifle.

I ended up content with the fact that one of my new CO2 clips was not working (again, Daisy Customer Service sent a free replacement). Otherwise, I would still be scratching my head about what could be causing the more severe ammo problems I’ve been reading about. The fortunate bottom line is that this provides a likely fix for people with MP4s that are misfiring or jamming. Order a replacement CO2 clip from Daisy or Winchester Customer Service and see if that doesn’t remedy the problem.

Eliminating minor misfires
Although I never experienced a major ammo problem or jam, except while testing CO2 clip 2, I was still having minor misfires (firing a blank or a skipped pellet left in the ammunition magazine when done shooting). This was occurring about once every one or two magazines (or once every 16 to 32 shots if you’re counting — roughly 5% of the time). I wanted to eliminate this if I could. When I contacted Daisy Customer Service to order the extra CO2 clips, I inquired about this. While the Daisy rep did not acknowledge a known ammo feed issue with the MP4, I not only received some suggestions over the phone, but a follow-up email with additional information, as well.

Winchester MP4 CO2 rifle skipped pellet
Except for testing CO2 clip 2, all of my own ammo feed problems were limited to infrequent misfires (blank shots) and an occasional skipped pellet that remained in a supposedly empty ammunition magazine.

Daisy cautions that you should use good-fitting (tight) pellets and make sure they’re seated all the way. This will prevent pellets from backing out of the magazine (more specifically the rotary cylinder), causing a jam. I’ve been using a Pellet Pen with Pellet Seater for loading, and the advice makes sense. However, none of the pellets I tested were loose, and most actually fit quite tightly. Ironically, the only pellet that caused a problem was Winchester’s own hollowpoint, which stuck out the front of the cylinder (even when fully seated) just enough to interfere with the cylinder’s rotation. I simply pushed the pellet noses back in slightly and didn’t experience any misfires during subsequent accuracy testing.

Despite how tightly most pellets fit, however, if I pulled an ammo mag that still had pellets in it I sometimes noticed that pellets I had seated all the way into the cylinder were loose and pushed back a little. On one occasion, I actually had a loosened pellet fall backwards right out of the magazine. I could not determine what might actually be pushing pellets backwards in their cylinder cavities, but my first guess is that CO2 bypass somewhere must be exerting pressure on the front of the pellets. The gun’s mild recoil (or possibly the bolt recocking action) might be another possibility. Whatever the cause, once this happens previously stopper-tight pellets will slide easily in the cylinder. As far as I could determine, though, pellet fit was not a problem in my gun. And it was not the problem for Pyramyd Air reviewers who tried a range of pellets with all kinds of persistent problems, either — that was probably the CO2 clip.

Winchester MP4 CO2 rifle loading pellets
I went to great lengths to load each pellet the same.

Winchester MP4 CO2 rifle rotary cylinder
Use a pellet seater to seat pellets fully into the rotary cylinder. A very tiny ridge (arrow) stops the pellet skirt within each individual cylinder chamber.

Daisy’s other — and I think more relevant — suggestion was to shoot slower, allowing 3-5 seconds between shots to let the CO2 cartridges recover. My first thought was that this takes away a lot of the fun of a semi-auto. This specific feature was one of the reasons I’d purchased the MP4 to begin with. Of course, the first thing my wife did as soon as she got her hands on my new gun was see how fast she could make me work the reset cord on our knockdown target. Sure enough, she had a skipped pellet in the magazine following her quick-fire volley. That’s not quite fun.

My second thought, in the form of a tiny bell ringing in the back of my mind, was that during my chronograph tests when I was waiting a full minute between shots, I didn’t have a single misfire for almost 150 rounds. I thought this was an anomaly, but it wasn’t!

With this advice in hand, I continued my testing, making a point to take time to breathe several times between shots. Lo and behold, I went through nearly 600 pellets with only 4 misfires, and I believe I actually caused these. Two of the misfires were from shooting fast during some other testing, and the other two are discussed below. Slowing down my shooting has essentially eliminated all my misfires—though I’m not having quite as much fun with the semi-auto MP4 as I was before.

Now, as to those final two misfires. After ejecting a supposedly empty ammunition magazine and discovering a skipped pellet still present, I remembered that on one shot I’d partially depressed the trigger, run out of “breath” before I was ready to shoot and released the trigger for another try. When I later removed the CO2 clip, I inverted the gun and squinted down into the receiver. As I squeezed the trigger, sure enough, I saw the catch that indexes the rotary cylinder move. So, squeezing the trigger indexes the ammo mag cylinder, and I’d inadvertently rotated a pellet out of queue, causing a skipped pellet. This revelation occurred early in my latest round of testing, and I continued shooting with steady, deliberate trigger pulls after that (and tried to make sure I didn’t run out of “breath” again). This also means that you should fully release the trigger between shots, though this was not a problem for me as far as I could tell. More deliberate trigger work, along with slower pacing between shots, has resulted in no more misfires so far.

Winchester MP4 CO2 rifle cylinder indexing
This rectangular catch (shown by the large arrow) just under the breech indexes the rotary cylinder on the ammunition magazine when the trigger is pulled. The inset photo and small arrow show the ratchet teeth on the rotary cylinder that the catch engages. A false start on a trigger pull can rotate the cylinder without actually firing, causing a pellet to be skipped in the firing sequence.

In summary, misaligned CO2 clips appear to be causing the most severe ammo feed problems in the Winchester MP4, and a replacement CO2 clip should get a malfunctioning MP4 working correctly. Tight-fitting pellets, slower shooting and more deliberate trigger pulls can eliminate minor misfires; but these require additional time and concentration and take some of the fun out of shooting this semi-auto. While I really like the Winchester MP4 and continue to enjoy shooting it, I’m having to jump through hoops to make it work properly, which is something prospective owners need to consider.

In Part 4, I’ll complete my accuracy testing (and finally break the half-inch barrier) and wrap up my evaluation.